Fix static analysis after main merge

- Drop unused StdioTransport import (special case removed in Client.new())
- Add ty:ignore to registry test assignment (type: ignore is mypy-only)

Author: jlowin

src/fastmcp/client/client.py

@@ -70,7 +70,6 @@
     PythonStdioTransport,
     SessionKwargs,
     SSETransport,
-    StdioTransport,
     StreamableHttpTransport,
     infer_transport,
 )

tests/client/client/test_client.py

@@ -774,7 +774,7 @@ def test_client_new_resets_mutable_task_state(fastmcp_server):
     """Client.new() should not share mutable task tracking structures."""
     client = Client(transport=FastMCPTransport(fastmcp_server))
 
-    client._task_registry["task-1"] = lambda: None  # type: ignore[assignment]
+    client._task_registry["task-1"] = lambda: None  # type: ignore[assignment]  # ty:ignore[invalid-assignment]
     client._submitted_task_ids.add("task-1")
 
     clone = client.new()