Add type annotations for windows_pipes and its test

[CoolCat467]

This PR adds type annotations for _windows_pipes.py and _tests/test_windows_pipes.py.

[codecov]

Codecov Report

Merging #2812 (5c4529c) into master (b6e1698) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2812   +/-   ##
=======================================
  Coverage   99.13%   99.13%           
=======================================
  Files         115      115           
  Lines       17230    17230           
  Branches     3084     3084           
=======================================
  Hits        17081    17081           
  Misses        104      104           
  Partials       45       45           

Files	Coverage Δ
trio/_tests/test_windows_pipes.py	100.00% <100.00%> (ø)
trio/_windows_pipes.py	100.00% <100.00%> (ø)

[A5rocks]

Looks simple enough, just one small comment

[jakkdl]

Types on _windows_pipes.py looks trivially correct. The test seems overcomplicated and gives codecov misses, but otherwise perfectly fine as well.

[A5rocks]

nitpicks but overall looks good (I don't really get the = Any bits)

[jakkdl]

agh, why is codecov being so dumb. It's incredibly frustrating that you can't trust the warnings displayed in the files changed view