Add standalone entry point for tzst

Created a new main.py file as the standalone entry point for tzst, intended for PyInstaller builds. This script sets up the Python path and invokes the CLI main function.

main.py

@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+"""Standalone entry point for tzst - used for PyInstaller builds."""
+
+import os
+import sys
+
+# Add the src directory to the Python path
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "src"))
+
+from tzst.cli import main
+
+if __name__ == "__main__":
+    sys.exit(main())