Add file-based document store and vector store (#96)

* Modify docstore and vectorstore objects to be reconstructable
* Simplify the file docstore
* Use the simple file docstore and vector store in MVP

knowledgehub/llms/chats/langchain_based.py

@@ -101,10 +101,13 @@ class LCChatMixin:
             return self._kwargs[name]
         return getattr(self._obj, name)
 
-    def dump(self):
+    def dump(self, *args, **kwargs):
+        from theflow.utils.modules import serialize
+
+        params = {key: serialize(value) for key, value in self._kwargs.items()}
         return {
             "__type__": f"{self.__module__}.{self.__class__.__qualname__}",
-            **self._kwargs,
+            **params,
         }
 
     def specs(self, path: str):