Fix mypy issues.

[jeffsawatzky]

Description

Fixes the mypy issues.

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a schema change
• [ ] This change requires a documentation update

Testing Done

A clear and concise description of the new tests added to validate the change as well as any manual testing done.

Checklist

• [x] I have added tests that prove my change works as expected, and make test passes with no new errors or warnings
• [x] I have run make check to ensure no new errors or warnings
• [x] I have updated the docs, if applicable, and run make docs to ensure no new errors or warnings
• [x] I have performed a self-review of my own code
• [x] I have commented my code in particularly hard-to-understand areas

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.96970% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.31%. Comparing base (517f830) to head (7f9b286). Report is 7 commits behind head on develop.

Files with missing lines	Patch %	Lines
amazonorders/entity/order.py	77.77%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #22 +/- ## =========================================== + Coverage 90.43% 91.31% +0.88% =========================================== Files 16 16 Lines 972 990 +18 =========================================== + Hits 879 904 +25 + Misses 93 86 -7 ```

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[alexdlaird]

This is great, thank for taking the time to look at these issues. I had been ignoring them for now, since I disagreed with a lot of the things mypy was saying were "issues", and didn't want to cause regressions diving in to them.

Just a heads up that I won't be able to fully dive in to reviewing this PR for a week or two, very busy right now, and I want to make sure I give it the time it deserves. Thank you in advance for the contribution!

[alexdlaird]

Just a few comments. The primary blocker for me are the assert additions, if you could raise proper exceptions instead. Otherwise the other comments should be trivial fixes, then I'm good to merge. Thanks!

[alexdlaird]

I want to get the changes in develop out ASAP, since Amazon has UI changes coming that are breaking the current implementation, and I want to cut a new release. I plan to merge this PR to develop later tonight, then I will address the comments I left on it before pushing the changes in a release. Thanks for your contribution!