Remove imports from starlette outside try-except

Author: darkhaniop

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -8,11 +8,6 @@
 from typing import TYPE_CHECKING, Any
 
 from pydantic import ValidationError
-from sse_starlette.sse import EventSourceResponse
-from starlette.applications import Starlette
-from starlette.authentication import BaseUser
-from starlette.requests import Request
-from starlette.responses import JSONResponse, Response
 
 from a2a.auth.user import UnauthenticatedUser
 from a2a.auth.user import User as A2AUser