refactor: add future annotations import to types and internal modules.

Author: timof1308

src/google/adk/tools/mcp_tool/_internal.py

@@ -43,6 +43,7 @@
 import logging
 import re
 from typing import Any
+from __future__ import annotations
 
 logger = logging.getLogger("google_adk." + __name__)
 

src/google/adk/tools/mcp_tool/types.py

@@ -14,6 +14,7 @@
 
 from typing import Callable
 from typing import Dict
+from __future__ import annotations
 
 from ...agents.readonly_context import ReadonlyContext