fix: Avoid false negatives for TC001-003 related to typing.cast.

[Daverball]

Closes: #127

We could be more aggressive and like with annotations treat even unquoted casts as forward references for the purposes of TC001-003. But I'm not sure it's the right call. Going the other way and recording them as uses seems bad too, due to the conflicting TC004/TC006 errors that will create, so the status quo should be fine for now.

If we can properly handle forward references that's already a huge win.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.8%. Comparing base (7621d51) to head (a6361ea).
Report is 90 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #199     +/-   ##
=======================================
- Coverage   98.7%   96.8%   -2.0%     
=======================================
  Files          3       3             
  Lines        482     985    +503     
=======================================
+ Hits         476     954    +478     
- Misses         6      31     +25     

Files with missing lines	Coverage Δ
flake8_type_checking/checker.py	96.6% <100.0%> (-2.0%)	⬇️

... and 1 file with indirect coverage changes

[sondrelg]

Agree. This seems most sane 👌