Add type hint checking with mypy

[dstansby]

This is a starting point to work towards #443. It:

• Adds configuration to run mypy
• pre-commit-config.yaml to run the type checking using pre-commit.
• Fixes type checking errors so that running mypy at least passes on the current code base.

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[pep8speaks]

Hello @dstansby! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file numcodecs/compat.py:

Line 109:33: E261 at least two spaces before inline comment

• In the file numcodecs/lzma.py:

Line 9:44: E261 at least two spaces before inline comment

• In the file numcodecs/ndarray_like.py:

Line 4:47: E261 at least two spaces before inline comment

• In the file numcodecs/zfpy.py:

Line 8:25: E261 at least two spaces before inline comment

Comment last updated at 2024-05-07 11:58:59 UTC

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 3 lines in your changes missing coverage. Please review.

Project coverage is 99.81%. Comparing base (ab86bcc) to head (e518a56).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
numcodecs/tests/test_zarr3.py	87.50%	2 Missing ⚠️
numcodecs/checksum32.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #460      +/-   ##
==========================================
- Coverage   99.92%   99.81%   -0.12%     
==========================================
  Files          62       62              
  Lines        2692     2712      +20     
==========================================
+ Hits         2690     2707      +17     
- Misses          2        5       +3     

Files with missing lines	Coverage Δ
numcodecs/abc.py	100.00% <100.00%> (ø)
numcodecs/compat.py	100.00% <100.00%> (ø)
numcodecs/lzma.py	100.00% <100.00%> (ø)
numcodecs/ndarray_like.py	100.00% <100.00%> (ø)
numcodecs/registry.py	100.00% <100.00%> (ø)
numcodecs/tests/test_lzma.py	100.00% <100.00%> (ø)
numcodecs/tests/test_zfpy.py	100.00% <100.00%> (ø)
numcodecs/zarr3.py	100.00% <100.00%> (ø)
numcodecs/zfpy.py	100.00% <100.00%> (ø)
numcodecs/checksum32.py	98.86% <80.00%> (-1.14%)	⬇️
... and 1 more

[dstansby]

Since this has been floating around with no objections for a while now, I propose to self-merge after #524 is merged, unless anyone objects.

[dstansby]

@normanrz I had to fix some typing in the zarr3 code, so would be good if you could check this. Once this is merged I was planning on doing as new release so we can get the zarr3 stuff released.