Use CustomBaseModel on all endpoint models and make fields Optional

[CM000n]

If you take a look at the merge requests in this project, most of them were created by breaking model assumptions and setting individual fields to Optional.

This merge request introduces a CustomBaseModel that automatically generates None values for values that do not match the data types of the model assumptions. In addition, all data types of the fields in the models were set to Optional.

This does not immediately make things better, but at least an error is no longer immediately thrown if the model assumptions break. This means that the models and the mytoyota lib remain functional within the scope of the information available and can continue to be used by end users if Toyota changes something in the API again.

[codecov]

Codecov Report

Attention: Patch coverage is 99.77011% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.80%. Comparing base (5310e09) to head (25276ae).
Report is 1 commits behind head on master.

Files	Patch %	Lines
mytoyota/utils/models.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #365      +/-   ##
==========================================
+ Coverage   82.58%   82.80%   +0.22%     
==========================================
  Files          29       30       +1     
  Lines        1418     1442      +24     
==========================================
+ Hits         1171     1194      +23     
- Misses        247      248       +1     

Flag	Coverage Δ
unittests	82.80% <99.77%> (+0.22%)	⬆️

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