Apply stricter typing to this project

[klaasnicolaas]

This PR adds stricter typing test to the project

[codecov]

Codecov Report

Merging #138 (f38d939) into main (772c2ed) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #138   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines           80        80           
  Branches         8         8           
=========================================
  Hits            80        80           

Impacted Files	Coverage Δ
gridnet/gridnet.py	100.00% <100.00%> (ø)
gridnet/models.py	100.00% <100.00%> (ø)

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