[Daxia] [ FastAPI ] Add dynamic CORS origin validation

[daxia778]

/claim #763

Summary

• Add an opt-in DynamicCORSMiddleware while preserving the existing Starlette CORSMiddleware export.
• Support sync and async allow_origin_func callbacks for per-request origin decisions.
• Fall back to static allow_origins behavior when no callback is supplied.
• Add cors_max_age for preflight Access-Control-Max-Age configuration.

Demo

https://github.com/daxia778/Bounty-Hunters/releases/download/issue-763-demo-de0559bc/fastapi-dynamic-cors-763-demo-de0559bc.mp4

Validation

• UV_PYTHON=<Python 3.12> uv run python -m pytest tests/test_dynamic_cors_middleware.py -q
• UV_PYTHON=<Python 3.12> uv run ruff check fastapi/middleware/cors.py tests/test_dynamic_cors_middleware.py
• UV_PYTHON=<Python 3.12> uv run ruff format --check fastapi/middleware/cors.py tests/test_dynamic_cors_middleware.py
• git diff --check

[github-actions]

Unfortunately the changes in this PR didn't fully resolve the issue. Please rework your solution and submit a new pull request.

Make sure to review the acceptance criteria in the linked issue and verify all conditions are met before resubmitting. See CONTRIBUTING.md for guidelines.