fix: resolve linting issues in token efficiency implementation

- Fix ambiguous variable names (l → layer)
- Remove unused imports and variables
- Organize import statements

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/evolution/optimizer.py

@@ -23,7 +23,7 @@ from google import genai
 
 from src.config import Settings
 from src.db import init_db
-from src.logging.decision_logger import DecisionLog, DecisionLogger
+from src.logging.decision_logger import DecisionLogger
 
 logger = logging.getLogger(__name__)