:hammer: `mypy` type check `tools/`

[Jiaqi-Lv]

Add mpypy checks to:

• tiatoolbox/tools/__init__.py
• tiatoolbox/tools/stainextract.py
• tiatoolbox/tools/pyramid.py
• tiatoolbox/tools/tissuemask.py
• tiatoolbox/tools/graph.py

[codecov[bot]]

Codecov Report

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

Comparison is base (a1feb25) 99.91% compared to head (e9697f4) 99.91%.

:exclamation: Current head e9697f4 differs from pull request most recent head 9a76ead. Consider uploading reports for the commit 9a76ead to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #782 +/- ## ======================================== Coverage 99.91% 99.91% ======================================== Files 69 69 Lines 8518 8523 +5 Branches 1637 1639 +2 ======================================== + Hits 8511 8516 +5 Partials 7 7 ```

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[shaneahmed]

Thanks @Jiaqi-Lv