[zigpy-review-bot]

Summary

Removes leftover type variables that are defined but never used, as reported in #999.

Changes

• zha/async_.py: remove the unused _Ts = TypeVarTuple("_Ts") and its import.
• zha/application/gateway.py: remove the unused _R TypeVar and the TypeVar import.
• zha/application/helpers.py: remove the unused _T, _R and _P and the ParamSpec / TypeVar imports.

No behaviour change. The remaining type variables in the package are all referenced (checked per name with grep).

Testing

• ruff check / ruff format and mypy on zha/ are clean.
• tests/test_gateway.py, tests/test_async_.py and tests/test_application_helpers.py: 114 passed.

Fixes #999

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.48%. Comparing base (2da1a5b) to head (12f63a4).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1014      +/-   ##
==========================================
- Coverage   97.48%   97.48%   -0.01%     
==========================================
  Files          61       61              
  Lines       10870    10865       -5     
==========================================
- Hits        10597    10592       -5     
  Misses        273      273              

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