feat(typing): type App classes

[CaselIT]

This is a follow up of ##2271

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e5ada2f) to head (9ed7475).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2286   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           63        63           
  Lines         7330      7410   +80     
  Branches      1276      1278    +2     
=========================================
+ Hits          7330      7410   +80     

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[CaselIT]

sorry for the force push + squash, but it was starting to become a mess

[vytas7]

Thanks, LGTM now bar these triple ''' docstrings, I regret even starting that discussion 🤣
But we can revise them later, no need to block the whole PR.

CodeCov is hallucinating as usual, but I have manually verified coverage by running tox on your branch.

[CaselIT]

Thanks, LGTM now bar these triple ''' docstrings, I regret even starting that discussion 🤣

I actually think it's a lot nicer for reading the source code. Having to escape the """ is quite ugly