🐛 Fix double JSON parsing from request body

Remove the 'await request.json()' call which was inadvertently left in the routing path. This ensures that the body bytes are passed directly to Pydantic's validate_json via FastAPIOptimizedJsonBytes, bypassing unnecessary Python dict allocations entirely.

fastapi/routing.py

@@ -412,19 +412,20 @@ def get_request_handler(
                 else:
                     body_bytes = await request.body()
                     if body_bytes:
-                        json_body: Any = Undefined
+                        is_json_content = False
                         content_type_value = request.headers.get("content-type")
                         if not content_type_value:
                             if not actual_strict_content_type:
-                                json_body = await request.json()
+                                is_json_content = True
                         else:
                             message = email.message.Message()
                             message["content-type"] = content_type_value
                             if message.get_content_maintype() == "application":
                                 subtype = message.get_content_subtype()
                                 if subtype == "json" or subtype.endswith("+json"):
-                                    json_body = await request.json()
-                        if json_body != Undefined:
+                                    is_json_content = True
+                        
+                        if is_json_content:
                             body = FastAPIOptimizedJsonBytes(body_bytes)
                         else:
                             body = body_bytes