Add uv tool install (#4492)

This is the minimal "working" implementation. In summary, we:

- Resolve the requested requirements
- Create an environment at `$UV_STATE_DIR/tools/$name`
- Inspect the `dist-info` for the main requirement to determine its
entry points scripts
- Link the entry points from a user-executable directory
(`$XDG_BIN_HOME`) to the environment bin
- Create an entry at `$UV_STATE_DIR/tools/tools.toml` tracking the
user's request

The idea with `tools.toml` is that it allows us to perform upgrades and
syncs, retaining the original user request (similar to declarations in a
`pyproject.toml`). I imagine using a similar schema in the
`pyproject.toml` in the future if/when we add project-levle tools. I'm
also considering exposing `tools.toml` in the standard uv configuration
directory instead of the state directory, but it seems nice to tuck it
away for now while we iterate on it. Installing a tool won't perform a
sync of other tool environments, we'll probably have an explicit `uv
tool sync` command for that?

I've split out todos into follow-up pull requests:

- #4509 (failing on Windows)
- #4501 
- #4504 

Closes #4485

crates/install-wheel-rs/src/script.rs

@@ -9,10 +9,10 @@ use crate::{wheel, Error};
 /// A script defining the name of the runnable entrypoint and the module and function that should be
 /// run.
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
-pub(crate) struct Script {
-    pub(crate) name: String,
-    pub(crate) module: String,
-    pub(crate) function: String,
+pub struct Script {
+    pub name: String,
+    pub module: String,
+    pub function: String,
 }
 
 impl Script {
@@ -64,7 +64,7 @@ impl Script {
     }
 }
 
-pub(crate) fn scripts_from_ini(
+pub fn scripts_from_ini(
     extras: Option<&[String]>,
     python_minor: u8,
     ini: String,