Move package into src layout

saiki.py

@@ -1,6 +1,13 @@
 #!/usr/bin/env python3
 """Saiki CLI entrypoint."""
 
+import sys
+from pathlib import Path
+
+SRC_DIR = Path(__file__).resolve().parent / "src"
+if str(SRC_DIR) not in sys.path:
+    sys.path.insert(0, str(SRC_DIR))
+
 from saiki.cli import main