fix: make LITELLM_CLIENT_SPECIFIC_PARAMS a tuple to prevent TypeError

tuple + list raises TypeError in get_openai_client_cache_key. Also add
test coverage for get_openai_client_cache_key to catch type mismatches.

litellm/llms/openai/common_utils.py

@@ -168,12 +168,12 @@ class BaseOpenAILLM:
             f"is_async={client_initialization_params.get('is_async')}",
         ]
 
-        LITELLM_CLIENT_SPECIFIC_PARAMS = [
+        LITELLM_CLIENT_SPECIFIC_PARAMS = (
             "timeout",
             "max_retries",
             "organization",
             "api_base",
-        ]
+        )
         openai_client_fields = (
             BaseOpenAILLM.get_openai_client_initialization_param_fields(
                 client_type=client_type

tests/test_litellm/llms/openai/test_openai_common_utils.py

@@ -164,3 +164,14 @@ def test_get_openai_client_initialization_param_fields(client_type):
     assert isinstance(result, tuple)
     assert len(result) > 0
     assert "self" not in result
+
+
+@pytest.mark.parametrize("client_type", ["openai", "azure"])
+def test_get_openai_client_cache_key(client_type):
+    """Verify get_openai_client_cache_key doesn't raise on tuple + tuple concatenation."""
+    key = BaseOpenAILLM.get_openai_client_cache_key(
+        client_initialization_params={"api_key": "sk-test"},
+        client_type=client_type,
+    )
+    assert isinstance(key, str)
+    assert "api_key=sk-test" in key