Change occurrences of format() to f-strings

[DimitriPapadopoulos]

Also change one occurrence of % to format(), as changing to an f-string would result in a very long line.

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

Merging #439 (d781c17) into main (515d097) will not change coverage.
The diff coverage is 100.00%.

❗ Current head d781c17 differs from pull request most recent head 7261c1e. Consider uploading reports for the commit 7261c1e to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #439   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           56        56           
  Lines         2242      2241    -1     
=========================================
- Hits          2242      2241    -1     

Files	Coverage Δ
numcodecs/abc.py	100.00% <100.00%> (ø)
numcodecs/compat.py	100.00% <100.00%> (ø)
numcodecs/delta.py	100.00% <100.00%> (ø)
numcodecs/json.py	100.00% <100.00%> (ø)
numcodecs/tests/common.py	100.00% <100.00%> (ø)
numcodecs/zfpy.py	100.00% <100.00%> (ø)