feat: pythonw support on gui scripts

[samypr100]

Summary

Closes #2956

This changes the bootstrap launcher script to use pythonw.exe instead of python.exe on gui_scripts via a helper fn both in the shebang and the python exe path encoded before UVUV magic, that way uv-trampoline's find_python_exe can use the right pythonw executable.

Test Plan

New unit tests for the helper was added.
Tested on example from #2956 on Windows to make sure it works as expected.

Questions

I noticed the docs in fn windows_script_launcher says The launcher will look for `python[w].exe` adjacent to it in the same directory to start the embedded script. but I didn't find such functionality when I looked in uv-trampoline.
I only saw clear_app_starting_state getting called when is_gui is set.

Was the intention to do this in uv-trampoline at some point instead?

[konstin]

I noticed the docs in fn windows_script_launcher says The launcher will look for python[w].exe adjacent to it in the same directory to start the embedded script. but I didn't find such functionality when I looked in uv-trampoline.

Thanks, that's indeed wrong, i removed it.

[charliermarsh]

Nice, thank you for this @samypr100!