Remove some mypy excludes

[puddly]

Typing is not actually enabled because we do not expose py.typed.

Progress:

• arg-type
• assignment
• attr-defined
• call-arg
• dict-item
• index
• misc
• no-any-return
• no-untyped-call
• no-untyped-def
• override
• return-value
• union-attr
• var-annotated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.30%. Comparing base (a77caee) to head (fbf254f).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #59      +/-   ##
==========================================
- Coverage   95.37%   95.30%   -0.07%     
==========================================
  Files          61       61              
  Lines        9337     9268      -69     
==========================================
- Hits         8905     8833      -72     
- Misses        432      435       +3     

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[puddly]

Save for deleted constants, these changes should all be lib-internal.

[dmulcahey]