Another round of mypy fixes

[jacobtomlinson]

More changes towards #381.

Down to 49 errors after this.

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.

Project coverage is 95.32%. Comparing base (87063fc) to head (3004635).
Report is 118 commits behind head on main.

Files with missing lines	Patch %	Lines
kr8s/_portforward.py	82.35%	3 Missing ⚠️
kr8s/_api.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
+ Coverage   94.61%   95.32%   +0.70%     
==========================================
  Files          29       30       +1     
  Lines        3141     3639     +498     
==========================================
+ Hits         2972     3469     +497     
- Misses        169      170       +1     

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