tests: add --strict-optional flag for dependency-gated skips

[mayaecht]

This change adds a strict mode for optional test dependencies.

When enabled, tests that would normally be skipped due to missing
optional dependencies fail instead, making missing test prerequisites
visible in CI and local development environments.

Changes include:

• support for strict optional dependency enforcement
• environment variable support to enable strict mode
• dependency reporting improvements
• documentation updates
• unit tests covering default and strict behavior

Tests:
pytest test/test_strict_optional.py -v
21 passed

[csutherl]

You shouldn't commit the __pycache__ dirs. The httpd .gitignore seems insufficient to catch them as deeply embedded in the dir structure as they are. Maybe incorporate some of the standard python .gitignore from https://github.com/github/gitignore/blob/main/Python.gitignore and retry to see if that cleans it up? Alternatively you could ditch test/__pycache__ and just use __pycache__/ I think.