fix: use typing_extensions.Self for Python 3.10 compatibility

- Replace try/except import block with direct typing_extensions import
- Follows same pattern as other files in codebase
- Resolves mypy type-checker failures on Python 3.10

Co-Authored-By: João <joao@crewai.com>

src/crewai/lite_agent.py

@@ -9,10 +9,7 @@ from typing import (
     get_origin,
 )
 
-try:
-    from typing import Self
-except ImportError:
-    from typing_extensions import Self
+from typing_extensions import Self
 
 from pydantic import (
     UUID4,