Support python find --script (#11891)

## Summary

Resolves #11794.

When `uv python find` is given a `--script` option, either the existing
environment for that script or the Python executable that would be used
to create it will be returned. If neither are found, the command exits
with exit code 1.

`--script` is incompatible with all other options to the same command.

## Test Plan

Unit tests.

docs/reference/cli.md

@@ -5018,6 +5018,8 @@ uv python find [OPTIONS] [REQUEST]
 
 </dd><dt id="uv-python-find--quiet"><a href="#uv-python-find--quiet"><code>--quiet</code></a>, <code>-q</code></dt><dd><p>Do not print any output</p>
 
+</dd><dt id="uv-python-find--script"><a href="#uv-python-find--script"><code>--script</code></a> <i>script</i></dt><dd><p>Find the environment for a Python script, rather than the current project</p>
+
 </dd><dt id="uv-python-find--system"><a href="#uv-python-find--system"><code>--system</code></a></dt><dd><p>Only find system Python interpreters.</p>
 
 <p>By default, uv will report the first Python interpreter it would use, including those in an active virtual environment or a virtual environment in the current working directory or any parent directory.</p>