fix: resolve CI/CD linting issues

- Remove unused imports (F401) from analyzers and test files
- Remove unused typing imports (Any, Dict, List, Optional)
- Remove unused datetime imports
- Remove unused rich.columns import
- Remove unused pytest imports in test files

src/git_insights.py

@@ -1,6 +1,6 @@
 from dataclasses import dataclass
 from datetime import datetime
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, Optional
 
 from src.analyzers.commit_pattern import CommitPatternAnalyzer
 from src.analyzers.code_churn import CodeChurnAnalyzer