Fix Ruff lint violations

[timkpaine]

Updates Python source and tests to satisfy diagnostics exposed by the current Ruff release while leaving the Ruff configuration unchanged.

• Modernize type annotations and dictionary construction.
• Use precise runtime exceptions and consistent integer parsing for RAYDAR_PORT.
• Remove invalid formatter suppression comments and simplify nested conditionals.
• Constrain FastAPI below 0.139.2 because FastAPI 0.139.2+ adds lock-bearing app state that Ray 2.56.1 cannot serialize for @serve.ingress.

Validation:

• make lint
• python -m build -w -n
• Clean isolated install with FastAPI 0.139.1 and Ray 2.56.1 successfully imports and serializes the Raydar app.

make test-py was also attempted locally, but Ray Serve could not bind 127.0.0.1:8000 because an existing VS Code Code Helper process owns that port; the second test consequently reached that unrelated listener.

[github-actions]

Test Results

2 tests  ±0   2 ✅ ±0   48s ⏱️ -1s
1 suites ±0   0 💤 ±0 
1 files   ±0   0 ❌ ±0 

Results for commit 2169a15. ± Comparison against base commit e8a6338.