fix: correct Context type parameters across examples and tests (#2256)

tests/client/test_list_roots_callback.py

@@ -25,7 +25,7 @@ async def test_list_roots_callback():
         return callback_return
 
     @server.tool("test_list_roots")
-    async def test_list_roots(context: Context[None], message: str):
+    async def test_list_roots(context: Context, message: str):
         roots = await context.session.list_roots()
         assert roots == callback_return
         return True