fix: PickleCoder and add tests for it.

tests/test_codecs.py

@@ -0,0 +1,22 @@
+from typing import Any
+
+import pytest
+
+from fastapi_cache.coder import PickleCoder
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        1,
+        "some_string",
+        (1, 2),
+        [1, 2, 3],
+        {"some_key": 1, "other_key": 2},
+    ],
+)
+def test_pickle_coder(value: Any) -> None:
+    encoded_value = PickleCoder.encode(value)
+    assert isinstance(encoded_value, str)
+    decoded_value = PickleCoder.decode(encoded_value)
+    assert decoded_value == value