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## Summary
Fix WindowsRunnable::from_script_path to correctly append extensions
instead of replacing them when resolving executable paths. This resolves
https://github.com/astral-sh/uv/issues/15165#issue-3304086689.
- Add add_extension_to_path helper that appends extensions properly
- Update extension resolution to use the new helper
- Add tests
## Test Plan
Added unit tests for the new and existing functionality that the change
touches. Tested manually locally on Windows.
<!-- How was it tested? -->
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Co-authored-by: Zanie Blue <contact@zanie.dev>
