Clean up packaging

[ericpre]

Keeping in draft for now, as it would be to get #123 merged first.

Progress of the PR

• Use declarative approach to define packaging in pyproject.toml and keep setup.py to compile c extension
• Consolidate MANIFEST.in. and pyproject.toml
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• add tests - build workflow,
• Rebase after Remove packaging of test data and download them on demand #123 is merged
• ready for review.

[codecov]

Codecov Report

Patch coverage: 76.47% and project coverage change: -0.25 ⚠️

Comparison is base (45ee267) 85.24% compared to head (716863e) 85.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
- Coverage   85.24%   85.00%   -0.25%     
==========================================
  Files          73       73              
  Lines        9042     9054      +12     
  Branches     2046     2049       +3     
==========================================
- Hits         7708     7696      -12     
- Misses        872      892      +20     
- Partials      462      466       +4     

Impacted Files	Coverage Δ
rsciio/edax/_api.py	88.80% <ø> (ø)
rsciio/__init__.py	85.71% <69.23%> (-14.29%)	⬇️
rsciio/_version.py	100.00% <100.00%> (ø)
rsciio/msa/_api.py	80.45% <100.00%> (ø)
rsciio/ripple/_api.py	69.93% <100.00%> (ø)

... and 1 file with indirect coverage changes

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