Improve interactions with existing Python executables during install (#8733)

Previously, we'd use the `--reinstall` flag to determine if we should
replace existing Python executables in the bin directory during an
install. There are a few problems with this:

- We replace executables we don't manage
- We can replace executables from other uv Python installations during
reinstall (surprising)
- We don't do the "right" thing when installing patch versions e.g.
installing `3.12.4` then `3.12.6` would fail without the reinstall flag

In `uv tool`, we have separate `--force` and `--reinstall` concepts.
Here we separate the flags (`--force` was previously just a
`--reinstall` alias) and add inspection of the existing executables to
inform a decision on replacement.

In brief, we will:

- Replace any executables with `--force`
- Replace executables for the same installation with `--reinstall`
- Replace executables for an older patch version by default

docs/reference/cli.md

@@ -4384,6 +4384,12 @@ uv python install [OPTIONS] [TARGETS]...
 
 <p>See <code>--project</code> to only change the project root directory.</p>
 
+</dd><dt><code>--force</code>, <code>-f</code></dt><dd><p>Replace existing Python executables during installation.</p>
+
+<p>By default, uv will refuse to replace executables that it does not manage.</p>
+
+<p>Implies <code>--reinstall</code>.</p>
+
 </dd><dt><code>--help</code>, <code>-h</code></dt><dd><p>Display the concise help for this command</p>
 
 </dd><dt><code>--native-tls</code></dt><dd><p>Whether to load TLS certificates from the platform&#8217;s native certificate store.</p>