Enable some stricter typing rules

[dstansby]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.70%. Comparing base (d8d53bb) to head (823b044).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #679   +/-   ##
=======================================
  Coverage   99.70%   99.70%           
=======================================
  Files          62       62           
  Lines        2751     2751           
=======================================
  Hits         2743     2743           
  Misses          8        8           

Files with missing lines	Coverage Δ
numcodecs/checksum32.py	100.00% <100.00%> (ø)