fix: use typing_extensions Self for telemetry

Author: Wondr-design

src/a2a/utils/telemetry.py

@@ -61,11 +61,7 @@ def internal_method(self):
 from collections.abc import Callable
 from typing import TYPE_CHECKING, Any
 
-
-try:
-    from typing import Self
-except ImportError:  # pragma: no cover - for Python < 3.11
-    from typing_extensions import Self
+from typing_extensions import Self
 
 
 if TYPE_CHECKING: