Convert class properties to class methods

[dstansby]

See changelog entry for motivation. Fixes #553

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 (42f89d2) to head (18f5f37).
Report is 70 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #578   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          59       59           
  Lines        2334     2334           
=======================================
  Hits         2332     2332           
  Misses          2        2           

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

[QuLogic]

Thanks! I backported this PR and successfully built on Python 3.13.