Add --gui-script flag for running Python scripts with pythonw.exe on … (#9152)

Addresses #6805

## Summary

This PR adds a `--gui-script` flag to `uv run` that allows running
Python scripts with `pythonw.exe` on Windows, regardless of file
extension. This solves the issue where users need to maintain duplicate
`.py` and `.pyw` files to run the same script with and without a console
window.

The implementation follows the pattern established by the existing
`--script` flag, but uses `pythonw.exe` instead of `python.exe` on
Windows. On non-Windows platforms, the flag is present but returns an
error indicating it's Windows-only functionality.

Changes:
- Added `--gui-script` flag (Windows-only)
- Added Windows test to verify GUI script behavior
- Added non-Windows test to verify proper error message
- Updated CLI documentation


## Test Plan

The changes are tested through:

1. New Windows-specific test that verifies:
- Script runs successfully with `pythonw.exe` when using `--gui-script`
- Console output is suppressed in GUI mode but visible in regular mode
   - Same script can be run both ways without modification

2. New non-Windows test that verifies:
- Appropriate error message when `--gui-script` is used on non-Windows
platforms

3. Documentation updates to clearly indicate Windows-only functionality

---------

Co-authored-by: Zanie Blue <contact@zanie.dev>

docs/reference/cli.md

@@ -184,6 +184,10 @@ uv run [OPTIONS] [COMMAND]
 
 <p>May be provided multiple times.</p>
 
+</dd><dt><code>--gui-script</code></dt><dd><p>Run the given path as a Python GUI script.</p>
+
+<p>Using <code>--gui-script</code> will attempt to parse the path as a PEP 723 script and run it with pythonw.exe, irrespective of its extension. Only available on Windows.</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>