feat: add python-disable-gunicorn flag

[IzaakGough]

Fixes #6628

[gemini-code-assist]

Code Review

This pull request introduces a --python-disable-gunicorn option to the Firebase emulators, allowing Python Functions to run using the Flask server in non-debug mode instead of gunicorn to prevent fork-safety crashes on macOS. This is implemented by dynamically injecting a sitecustomize.py shim via PYTHONPATH to intercept and block gunicorn imports. The feedback recommends improving the Python import hook's robustness by using *args and **kwargs to support varying signatures, and registering a process exit hook to clean up the temporary directory created for the shim to prevent resource leaks.

[gemini-code-assist]

The _firebase_import_without_gunicorn hook currently uses a fixed signature (name, globals=None, locals=None, fromlist=(), level=0). To ensure maximum compatibility across different Python versions, alternative interpreters, or third-party packages that might call __import__ with different positional/keyword arguments, it is more robust to use *args and **kwargs and extract the name argument dynamically.

Suggested change

	def _firebase_import_without_gunicorn(name, globals=None, locals=None, fromlist=(), level=0):
	if name == "functions_framework._http.gunicorn":
	raise ImportError("Gunicorn disabled for local Firebase Functions emulator")
	return _original_import(name, globals, locals, fromlist, level)
	def _firebase_import_without_gunicorn(*args, **kwargs):
	name = args[0] if args else kwargs.get("name")
	if name == "functions_framework._http.gunicorn":
	raise ImportError("Gunicorn disabled for local Firebase Functions emulator")
	return _original_import(*args, **kwargs)