`mypy`: `--strict` type checking

[tony]

https://github.com/cihai/unihan-etl/pull/257, https://github.com/cihai/unihan-db/pull/298, https://github.com/cihai/cihai/pull/324, https://github.com/cihai/cihai-cli/pull/277

Ramp up type safety / create a typed library

[codecov[bot]]

Codecov Report

Merging #257 (56a2066) into master (3f518e1) will increase coverage by 1.14%. The diff coverage is 98.56%.

:exclamation: Current head 56a2066 differs from pull request most recent head e319e5b. Consider uploading reports for the commit e319e5b to get more accurate results

@@            Coverage Diff             @@
##           master     #257      +/-   ##
==========================================
+ Coverage   92.67%   93.82%   +1.14%     
==========================================
  Files          10       11       +1     
  Lines         833     1036     +203     
==========================================
+ Hits          772      972     +200     
- Misses         61       64       +3     

Impacted Files	Coverage Δ
docs/conf.py	58.13% <33.33%> (-0.69%)	:arrow_down:
tests/test_unihan.py	97.71% <96.07%> (-1.06%)	:arrow_down:
unihan_etl/process.py	91.34% <96.49%> (+0.43%)	:arrow_up:
tests/conftest.py	94.44% <100.00%> (+0.56%)	:arrow_up:
tests/test_expansion.py	99.25% <100.00%> (+<0.01%)	:arrow_up:
tests/test_util.py	100.00% <100.00%> (ø)
unihan_etl/constants.py	100.00% <100.00%> (ø)
unihan_etl/expansion.py	100.00% <100.00%> (ø)
unihan_etl/test.py	100.00% <100.00%> (ø)
unihan_etl/types.py	100.00% <100.00%> (ø)

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