refactor(types): auto -> None sweep across entire codebase

Applied 236 return type annotations to functions with no return values
across 100+ files (core modules, tests, scripts, simulations).
Added Phase 4 to python_style_refactor track for remaining 597 items
(untyped params, vars, and functions with return values).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_gemini_metrics.py

@@ -9,7 +9,7 @@ sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__), "..")))
 # Import the necessary functions from ai_client, including the reset helper
 from ai_client import get_gemini_cache_stats, reset_session
 
-def test_get_gemini_cache_stats_with_mock_client():
+def test_get_gemini_cache_stats_with_mock_client() -> None:
  """
     Test that get_gemini_cache_stats correctly processes cache lists
     from a mocked client instance.