fix: resolve CI linting issues across codebase

- Remove unused imports (sys, Path, defaultdict, etc.)
- Convert Optional types to modern | syntax
- Fix trailing whitespace and blank line whitespace issues
- Sort imports alphabetically
- Add __future__ annotations for type syntax support

src/codesnap/__init__.py

@@ -0,0 +1,13 @@
+from codesnap.core.analyzer import CodeAnalyzer
+from codesnap.core.complexity import ComplexityCalculator
+from codesnap.core.dependency_graph import DependencyGraph
+from codesnap.core.models import DependencyInfo, FileSummary, FunctionInfo
+
+__all__ = [
+    "CodeAnalyzer",
+    "ComplexityCalculator",
+    "DependencyGraph",
+    "DependencyInfo",
+    "FileSummary",
+    "FunctionInfo",
+]