Use CFFI's out-of-line mode for import time reductions on Windows

[A5rocks]

Turns out parsing C takes time! Relevant charts (from before this):

(x axis is import time in microseconds, excluding anything that module itself imports)

I know there's conflicts but I'll wait until CI is fixed anyways.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (8771618) to head (33ed865).
⚠️ Report is 53 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3263   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             127          127           
  Lines           19270        19266    -4     
  Branches         1300         1301    +1     
===============================================
- Hits            19270        19266    -4     

Files with missing lines	Coverage Δ
src/trio/_core/_io_windows.py	100.00000% <ø> (ø)
src/trio/_core/_tests/test_windows.py	100.00000% <100.00000%> (ø)
src/trio/_core/_windows_cffi.py	100.00000% <100.00000%> (ø)

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[jakkdl]

maybe add typing-only hints to avoid breaking typing for end users?

[A5rocks]

This shouldn't break any typing for end users because it's unexported, but also the reason there's type ignores is because typeshed's stubs are wrong.

[A5rocks]

I don't quite get why mypy is failing in CI since I can't repro that locally. Maybe I need to make my environment more similar?

[jakkdl]

I don't quite get why mypy is failing in CI since I can't repro that locally. Maybe I need to make my environment more similar?

have you tried tox -e typing? (I repro the error when I do)

[A5rocks]

Turns out that's the difference between an editable and non-editable install! Scary.

[jakkdl]

ah, yeah editable installs can confuse static analysis. I remember having a lot of problems with pyright --verifytypes caused by it

[jakkdl]

Looks good as far as I can tell, feel free to merge when ready imo.