fix(responses): add models to TypedDict and fix test state corruption

- Add 'models' field to ResponsesAPIOptionalRequestParams TypedDict so
  the Perplexity fallback chain param is not silently filtered out by
  get_requested_response_api_optional_param(). Verified with curl that
  Perplexity's models param works (tries models in order until one
  succeeds).
- Fix test_python_class_takes_priority_over_json: save and restore the
  original JSONProviderRegistry entry instead of deleting it, preventing
  state corruption for subsequent tests.

litellm/types/llms/openai.py

@@ -1155,6 +1155,8 @@ class ResponsesAPIOptionalRequestParams(TypedDict, total=False):
     ]  # Number of partial images to generate (1-3) for streaming image generation
     context_management: Optional[List[ContextManagementEntry]]
     """Context management configuration. E.g. [{\"type\": \"compaction\", \"compact_threshold\": 200000}] for server-side compaction (minimum 1000)."""
+    models: Optional[List[str]]
+    """Model fallback chain (e.g. Perplexity). Models are tried in order until one succeeds."""
 
 
 class ResponsesAPIRequestParams(ResponsesAPIOptionalRequestParams, total=False):

tests/test_litellm/llms/openai_like/responses/test_openai_like_responses.py

@@ -325,6 +325,7 @@ class TestProviderConfigManagerResponsesAPI:
                 "supported_endpoints": ["/v1/responses"],
             },
         )
+        original = JSONProviderRegistry._providers.get("perplexity")
         JSONProviderRegistry._providers["perplexity"] = test_config
         try:
             config = ProviderConfigManager.get_provider_responses_api_config(
@@ -334,4 +335,7 @@ class TestProviderConfigManagerResponsesAPI:
             # Should be the Python class, not the JSON-generated one
             assert isinstance(config, PerplexityResponsesConfig)
         finally:
-            del JSONProviderRegistry._providers["perplexity"]
+            if original is not None:
+                JSONProviderRegistry._providers["perplexity"] = original
+            else:
+                del JSONProviderRegistry._providers["perplexity"]