feat: Add allow_listing_models

• Add allow_listing_models configuration flag to VLLM provider to control model listing behavior
• Implement allow_listing_models() method across all providers with default implementations in base classes
• Prevent HTTP requests to /v1/models endpoint when allow_listing_models=false for improved security and performance
• Fix unit tests to include allow_listing_models method in test classes and mock objects

tests/unit/distribution/routers/test_routing_tables.py

@@ -52,6 +52,9 @@ class InferenceImpl(Impl):
     async def should_refresh_models(self):
         return False
 
+    async def allow_listing_models(self):
+        return True
+
     async def list_models(self):
         return [
             Model(