Update __init__.py (modelcontextprotocol#335)

Author: arthrod

src/mcp/server/__init__.py

@@ -1,4 +1,5 @@
 from .fastmcp import FastMCP
 from .lowlevel import NotificationOptions, Server
+from .models import InitializationOptions
 
-__all__ = ["Server", "FastMCP", "NotificationOptions"]
+__all__ = ["Server", "FastMCP", "NotificationOptions", "InitializationOptions"]