fix: allow StringParam for vpc_connector typing

[cabljac]

Description

Takes over #269 (all commits from @HassanBahati and @IzaakGough preserved). Widens the typing for the vpc_connector option to match the values already supported at runtime: str | Expression[str] | Sentinel | None, so StringParam and other string-valued params are type-correct.

The manifest generation logic is unchanged; it already serializes Expression[...] (including params) into CEL strings, so this is a typing alignment rather than a behavioral change.

Related Issues:

Fixes #219
Supersedes #269

Changes Made

• Widened RuntimeOptions.vpc_connector in src/firebase_functions/options.py from str | Sentinel | None to str | Expression[str] | Sentinel | None.
• Aligned the set_global_options signature for vpc_connector and vpc_connector_egress_settings with the RuntimeOptions field types.
• Added parameterized tests in tests/test_options.py covering StringParam and other Expression values end to end (_asdict_with_global_options() and _endpoint() both produce the CEL string).
• Added a tests/conftest.py autouse fixture clearing the global params registry between tests, needed for the new parameterized tests and a general test-isolation improvement.

Testing Evidence

Validated in isolation and via the MRE.

Tests Run (if applicable)

• Unit tests
• Integration tests
• Manual testing

[gemini-code-assist]

Code Review

This pull request updates RuntimeOptions and set_global_options to allow vpc_connector to accept Expression[str] types (such as StringParam or ternary expressions), and adds corresponding unit tests. It also introduces pytest fixtures to clean up global options and parameters between tests. However, clearing the global params._params registry entirely in tests/conftest.py can delete module-level parameters from other test files, potentially causing test failures. It is recommended to capture and restore the registry's state instead of clearing it completely.

[gemini-code-assist]

Clearing params._params entirely between tests will delete any parameters declared at the module level in other test files (which are instantiated and registered when those test files are imported). This can cause subsequent tests that rely on those module-level parameters to fail with missing parameter errors or duplicate parameter errors if they are re-declared.

Instead of clearing the registry completely, we should capture the state of params._params before each test runs and restore it afterward. This preserves module-level parameters while still cleaning up any parameters declared dynamically inside individual tests.

Suggested change

	@pytest.fixture(autouse=True)
	def _cleanup_params():
	"""Clear the global params registry so each test runs with a clean state."""
	params._params.clear()
	yield
	params._params.clear()
	@pytest.fixture(autouse=True)
	def _cleanup_params():
	"""Reset the global params registry to its pre-test state so tests don't leak params."""
	original_params = params._params.copy()
	yield
	params._params.clear()
	params._params.update(original_params)

[cabljac]

Closing, #269 is the vehicle for this fix.