🔧 chore(schemas.py): add StreamData model and __str__ method to improve readability of stream data

The StreamData model is added to represent the data that is streamed from the server. The __str__ method is added to improve the readability of the stream data by returning a formatted string that includes the event and data attributes.

src/backend/langflow/api/v1/schemas.py

@@ -1,6 +1,7 @@
 from typing import Any, Dict, List, Optional, Union
 from langflow.database.models.flow import FlowCreate, FlowRead
 from pydantic import BaseModel, Field, validator
+import json
 
 
 class GraphData(BaseModel):
@@ -101,3 +102,11 @@ class InitResponse(BaseModel):
 
 class BuiltResponse(BaseModel):
     built: bool
+
+
+class StreamData(BaseModel):
+    event: str
+    data: dict
+
+    def __str__(self) -> str:
+        return f"event: {self.event}\ndata: {json.dumps(self.data)}\n\n"