Fixes #140914
Imports TypeVar from typing_extensions alongside ParamSpec so both type parameters use the same default-sentinel machinery when another vendored typing_extensions copy has monkeypatched typing internals. This preserves the existing CachedMethod[P, RV] convention while avoiding the import-time TypeError.
Test Plan:
python3 -m...
🛡️ VERIFIED CYBER INTELLIGENCE ID: #3569689