Adds crc32c codec

[normanrz]

Adds Crc32c codec, which appends a crc32c checksum to the input buffer when encoding and validates the checksum when decoding.

Fixes #610

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)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.91%. Comparing base (88464f6) to head (e133d0b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #613   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          59       59           
  Lines        2326     2405   +79     
=======================================
+ Hits         2324     2403   +79     
  Misses          2        2           

Files with missing lines	Coverage Δ
numcodecs/__init__.py	100.00% <100.00%> (ø)
numcodecs/checksum32.py	100.00% <100.00%> (ø)
numcodecs/tests/test_checksum32.py	100.00% <100.00%> (ø)

[dstansby]

Should this live in https://github.com/zarr-developers/numcodecs/blob/main/numcodecs/checksum32.py, where we already have CRC32? As I understand (from a stackoverflow post) CRC32 and CRC32C are basically the same algorithm, so it makes sense to put them in the same namespace.

[normanrz]

I didn't look for checksum32.py. Thanks for telling me.
I just looked into that. A problem is that the existing checksum codecs prepend the checksum whereas zarr3 expects the checksum to be appended. Either we single out crc32c to append the checksum or we add an option to all checksum codecs. Wdyt?

[normanrz]

I moved the code to checksum32.py and refactored the tests (they had no parameterization) in 7e78d93

[dstansby]

Looks good to me - just a few questions, but none of them blocking.

[normanrz]

I don't see why this PR isn't ready to merge (it might be just late)? Do I need another approval?

[dstansby]

Maybe just needs a fresh approval?