Improve type inference when using decorators with pyright

[breathe]

Problem

pyright infers the wrong types for functions which are decorated with @app.command or @app.default.

Use of TypeVar here allows to explicitly preserve the original type information of the original non-wrapped function argument which isn't modified in anyway by the decorators

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.40%. Comparing base (1f5e3d6) to head (037ddfd).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #172   +/-   ##
=======================================
  Coverage   96.40%   96.40%           
=======================================
  Files          16       16           
  Lines        1864     1865    +1     
  Branches      468      468           
=======================================
+ Hits         1797     1798    +1     
  Misses         29       29           
  Partials       38       38           

Flag	Coverage Δ
unittests	96.19% <100.00%> (+<0.01%)	⬆️

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[BrianPugh]

released with v2.6.2, thank you for the contribution!