feat: restore the last queue per server

tests/test_queue_repository.py

@@ -0,0 +1,25 @@
+import tempfile
+import unittest
+from pathlib import Path
+
+from zyrarbot.storage.queue_repository import QueueRepository
+
+
+class QueueRepositoryTest(unittest.TestCase):
+    def test_snapshots_are_isolated_per_guild(self):
+        with tempfile.TemporaryDirectory() as directory:
+            repository = QueueRepository(directory)
+            first = [{"id": "first", "title": "First", "plays_left": 2}]
+            second = [{"id": "second", "title": "Second", "plays_left": 4}]
+
+            repository.save(10, first)
+            repository.save(20, second)
+
+            self.assertEqual(repository.load(10), first)
+            self.assertEqual(repository.load(20), second)
+            self.assertTrue((Path(directory) / "10.json").exists())
+            self.assertTrue((Path(directory) / "20.json").exists())
+
+
+if __name__ == "__main__":
+    unittest.main()