Move package into src layout

tests/test_core.py

@@ -1,8 +1,14 @@
 from __future__ import annotations
 
 import os
+import sys
 import tempfile
 import unittest
+from pathlib import Path
+
+SRC_DIR = Path(__file__).resolve().parents[1] / "src"
+if str(SRC_DIR) not in sys.path:
+    sys.path.insert(0, str(SRC_DIR))
 
 from saiki.audio import build_playlist, resolve_media_paths
 from saiki.config import DEFAULT_CONFIG, deep_merge