🔧 mypy type check wsicore

[Jiaqi-Lv]

Fix typing for files in tiatoolbox/wsicore/

• tiatoolbox/wsicore/__init__.py
• tiatoolbox/wsicore/wsimeta.py
• tiatoolbox/wsicore/metadata/

Will work on tiatoolbox/wsicore/wsireader.py after #825

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.70%. Comparing base (c05a6b7) to head (5b50d2f).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #935   +/-   ##
========================================
  Coverage    99.70%   99.70%           
========================================
  Files           71       71           
  Lines         8851     8852    +1     
  Branches      1154     1154           
========================================
+ Hits          8825     8826    +1     
  Misses          23       23           
  Partials         3        3           

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