[Misc] Add __setitem__ for LazyDict (#10469)

Signed-off-by: Yanyi Liu <wolfsonliu@163.com>

vllm/utils.py

@@ -1491,6 +1491,9 @@ class LazyDict(Mapping, Generic[T]):
             self._dict[key] = self._factory[key]()
         return self._dict[key]
 
+    def __setitem__(self, key: str, value: Callable[[], T]):
+        self._factory[key] = value
+
     def __iter__(self):
         return iter(self._factory)