Type hint check and corrections

[oncleben31]

Add type hint checks with mypy and typeguard following best practices of hypermodern_python (see #18).
Code update was needed to correct all errors detected by mypy.

[Quentame]

Function typing in tests can be optional.

Don't know Nox and Poetry much, but seems nice otherwise.

[oncleben31]

Don't merge yet, I need to correct the GitHub workflow about code coverage.

[codecov]

Codecov Report

Merging #25 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #25   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          309       388   +79     
  Branches        19        24    +5     
=========================================
+ Hits           309       388   +79     

Impacted Files	Coverage Δ
src/meteofrance/client.py	100.00% <100.00%> (ø)
src/meteofrance/helpers.py	100.00% <100.00%> (ø)
src/meteofrance/model/forecast.py	100.00% <100.00%> (ø)
src/meteofrance/model/picture_of_the_day.py	100.00% <100.00%> (ø)
src/meteofrance/model/place.py	100.00% <100.00%> (ø)
src/meteofrance/model/rain.py	100.00% <100.00%> (ø)
src/meteofrance/model/warning.py	100.00% <100.00%> (ø)
src/meteofrance/session.py	100.00% <100.00%> (ø)

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[oncleben31]

Code coverage check in GA is OK now. We can merge as soon as the code review is done.