Forward FastAPI reload scope options

[dajiaohuang]

Summary

Fixes #3962.

Forward the reload scope options passed to the FastAPI backend to the spawned Uvicorn process. This makes reload_dirs, reload_excludes, and reload_includes effective while preserving existing defaults.

Tests

• pytest -q tests/backend_tests/test_preconfig_backends.py::test_fastapi_run_forwards_reload_scope
• python -m py_compile dash/backends/_fastapi.py tests/backend_tests/test_preconfig_backends.py

Checklist

• Tests pass
• Tests were added for the change

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dajiaohuang]

Triage update for the two failing checks on head 374bc45: Run performance benchmarks completed its benchmark work but failed only when the workflow token attempted to create/update the benchmark summary comment (403 Resource not accessible by integration); WebSocket Tests (Python 3.9) ran 70 tests successfully and had one Selenium/Chrome failure with javascript error: u.concat is not a function on Chrome 152. The remaining checks, including SonarCloud, pass. No source change was made because both failures are workflow/runner-environment symptoms; maintainer rerun or workflow adjustment is needed.

[T4rk1n]

Looks good, just need a changelog entry.