SQLAlchemy v2 + mypy strict typings / annotations

[tony]

Fixes #310, #312
Closes #298

See also:

• SQLAlchemy v2:
  • https://docs.sqlalchemy.org/en/20/changelog/migration_20.html
  • https://docs.sqlalchemy.org/en/20/changelog/whatsnew_20.html
  • SQLAlchemy v2 support cihai#340
• mypy:
  • --strict: https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-strict
  • Old PR: mypy: --strict type checking #298

[codecov]

Codecov Report

Merging #311 (8eaa5ea) into master (3db49b3) will decrease coverage by 21.55%.
The diff coverage is 34.89%.

@@             Coverage Diff             @@
##           master     #311       +/-   ##
===========================================
- Coverage   89.11%   67.57%   -21.55%     
===========================================
  Files           7        7               
  Lines         579      623       +44     
  Branches       79       79               
===========================================
- Hits          516      421       -95     
- Misses         51      197      +146     
+ Partials       12        5        -7     

Impacted Files	Coverage Δ
src/unihan_db/importer.py	2.14% <1.80%> (-80.77%)	⬇️
src/unihan_db/bootstrap.py	37.00% <48.38%> (-18.44%)	⬇️
src/unihan_db/tables.py	100.00% <100.00%> (ø)
tests/conftest.py	98.30% <100.00%> (+0.22%)	⬆️
tests/test_bootstrap.py	100.00% <100.00%> (ø)

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