:hammer: Add `mypy` Checks

[Jiaqi-Lv]

Files added:

• tiatoolbox/utils/exceptions.py
• tiatoolbox/utils/magic.py
• tiatoolbox/utils/metrics.py
• tiatoolbox/utils/transforms.py
• tiatoolbox/tiatoolbox.py

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1d3f039) 99.85% compared to head (d7d0450) 99.85%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #740 +/- ## ======================================== Coverage 99.85% 99.85% ======================================== Files 65 65 Lines 7520 7532 +12 Branches 1461 1461 ======================================== + Hits 7509 7521 +12 Misses 4 4 Partials 7 7 ```

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[shaneahmed]

@Jiaqi-Lv Please can you fix the coverage? The if statement only covers once condition in tests. Try modifying the tests to cover this scenario. https://app.codecov.io/gh/TissueImageAnalytics/tiatoolbox/pull/740/blob/tiatoolbox/utils/transforms.py#L110