Skip script collisions with entry points

[Himanshuagrawal4]

Summary

• track entry point scripts written during installation
• skip .data/scripts files that would overwrite an already generated entry point script
• emit a runtime warning for the skipped conflicting script
• add a regression test for a wheel containing both forms with the same script name

Closes #315.

Validation

• PYTHONPATH=src python -m pytest tests/test_core.py
• python -m compileall -q src\installer
• git diff --check

[eli-schwartz]

"In the face of ambiguity, refuse the temptation to guess."

[Himanshuagrawal4]

Thanks. I agree this is a policy choice. This PR follows one of the options from #315 and pip's current behavior: when a legacy script and generated entry point target the same script path, keep the generated entry point and skip the legacy script. Unlike pip, it emits a RuntimeWarning so callers can see that the wheel is ambiguous. Happy to change direction if maintainers prefer failing with a clearer error or exposing a policy knob instead.