Add support for UV_FROZEN and UV_LOCKED (#8340)

## Summary

Closes https://github.com/astral-sh/uv/issues/8321.

docs/reference/cli.md

@@ -160,6 +160,7 @@ uv run [OPTIONS] [COMMAND]
 
 <p>Instead of checking if the lockfile is up-to-date, uses the versions in the lockfile as the source of truth. If the lockfile is missing, uv will exit with an error. If the <code>pyproject.toml</code> includes changes to dependencies that have not been included in the lockfile yet, they will not be present in the environment.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -232,6 +233,7 @@ uv run [OPTIONS] [COMMAND]
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--module</code>, <code>-m</code></dt><dd><p>Run a Python module.</p>
 
 <p>Equivalent to <code>python -m &lt;module&gt;</code>.</p>
@@ -749,6 +751,7 @@ uv add [OPTIONS] <PACKAGES|--requirements <REQUIREMENTS>>
 
 <p>The project environment will not be synced.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -813,6 +816,7 @@ uv add [OPTIONS] <PACKAGES|--requirements <REQUIREMENTS>>
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>
@@ -1081,6 +1085,7 @@ uv remove [OPTIONS] <PACKAGES>...
 
 <p>The project environment will not be synced.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -1145,6 +1150,7 @@ uv remove [OPTIONS] <PACKAGES>...
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>
@@ -1401,6 +1407,7 @@ uv sync [OPTIONS]
 
 <p>Instead of checking if the lockfile is up-to-date, uses the versions in the lockfile as the source of truth. If the lockfile is missing, uv will exit with an error. If the <code>pyproject.toml</code> includes changes to dependencies that have not been included in the lockfile yet, they will not be present in the environment.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -1469,6 +1476,7 @@ uv sync [OPTIONS]
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>
@@ -1717,6 +1725,7 @@ uv lock [OPTIONS]
 <p>May also be set with the <code>UV_FIND_LINKS</code> environment variable.</p>
 </dd><dt><code>--frozen</code></dt><dd><p>Assert that a <code>uv.lock</code> exists, without updating it</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -1783,6 +1792,7 @@ uv lock [OPTIONS]
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>
@@ -2023,6 +2033,7 @@ uv export [OPTIONS]
 
 <p>If a <code>uv.lock</code> does not exist, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -2089,6 +2100,7 @@ uv export [OPTIONS]
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>
@@ -2338,6 +2350,7 @@ uv tree [OPTIONS]
 
 <p>If the lockfile is missing, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_FROZEN</code> environment variable.</p>
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--index</code> <i>index</i></dt><dd><p>The URLs to use when resolving dependencies, in addition to the default index.</p>
@@ -2406,6 +2419,7 @@ uv tree [OPTIONS]
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>
 
+<p>May also be set with the <code>UV_LOCKED</code> environment variable.</p>
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>
 
 <p>By default, uv loads certificates from the bundled <code>webpki-roots</code> crate. The <code>webpki-roots</code> are a reliable set of trust roots from Mozilla, and including them in uv improves portability and performance (especially on macOS).</p>