Fix generate accurate session_uri for nested SSE paths

Author: sebin1213

src/mcp/server/sse.py

@@ -37,6 +37,7 @@ async def handle_sse(request):
 from urllib.parse import quote
 from uuid import UUID, uuid4
 
+import re
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import ValidationError