Full typing for scrapy/spidermiddlewares.

[wRAR]

I've removed the or () parts because result shouldn never be None (well, because mypy said async for r in () is incorrect code and I looked at it closely).

[codecov]

Codecov Report

Merging #6130 (7857844) into master (593bfd8) will increase coverage by 0.02%.
The diff coverage is 90.67%.

❗ Current head 7857844 differs from pull request most recent head e54dc59. Consider uploading reports for the commit e54dc59 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6130      +/-   ##
==========================================
+ Coverage   88.71%   88.73%   +0.02%     
==========================================
  Files         160      160              
  Lines       11428    11473      +45     
  Branches     1862     1867       +5     
==========================================
+ Hits        10138    10181      +43     
  Misses        979      979              
- Partials      311      313       +2     

Files	Coverage Δ
scrapy/spidermiddlewares/depth.py	94.11% <88.23%> (-3.56%)	⬇️
scrapy/spidermiddlewares/httperror.py	95.45% <88.23%> (-4.55%)	⬇️
scrapy/spidermiddlewares/offsite.py	95.71% <90.90%> (-2.70%)	⬇️
scrapy/spidermiddlewares/urllength.py	84.37% <87.50%> (-3.63%)	⬇️
scrapy/spidermiddlewares/referer.py	92.54% <93.47%> (-0.70%)	⬇️

... and 1 file with indirect coverage changes