Add mypy test to CI

[zakajd]

Closes #160

Proposed Changes

• mypy.ini with proper config
• Fix existing errors
• Add test to CI

I had to add "--allow-redefinition" flag to ignore errors due to re-use of the same variable in the functions multiple times.
PyTorch is currently in progress of adding proper types, but currently there a lot of errors, so I ignore them (see mypy.ini file for details).

[codecov]

Codecov Report

Merging #180 into master will increase coverage by 0.04%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master     #180      +/-   ##
==========================================
+ Coverage   94.82%   94.87%   +0.04%     
==========================================
  Files          25       25              
  Lines        1699     1696       -3     
==========================================
- Hits         1611     1609       -2     
+ Misses         88       87       -1     

Flag	Coverage Δ
unittests	94.87% <96.42%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
piq/gs.py	74.35% <0.00%> (+0.94%)	⬆️
piq/brisque.py	99.03% <100.00%> (-0.01%)	⬇️
piq/fid.py	88.33% <100.00%> (ø)
piq/fsim.py	100.00% <100.00%> (ø)
piq/functional/colour_conversion.py	100.00% <100.00%> (ø)
piq/functional/layers.py	100.00% <100.00%> (ø)
piq/gmsd.py	100.00% <100.00%> (ø)
piq/haarpsi.py	100.00% <100.00%> (ø)
piq/kid.py	88.54% <100.00%> (ø)
piq/msid.py	77.07% <100.00%> (ø)
... and 5 more

[zakajd]

@snk4tr Ready for review

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication