MNT: Modernize packaging, etc

[pllim]

I could not run tests locally, then I realized the packaging state of this package is way outdated. This pull request is to:

• Modernize packaging.
• Turn unhandled warnings into exceptions.
• Update test matrix.
• Fix test package data.
• Handle test warnings.

Out of scope:

• 65

[codecov[bot]]

Codecov Report

Merging #64 (2c93f45) into main (7f3229d) will increase coverage by 0.32%. The diff coverage is 87.50%.

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   95.80%   96.13%   +0.32%     
==========================================
  Files          15       15              
  Lines        1145     1139       -6     
==========================================
- Hits         1097     1095       -2     
+ Misses         48       44       -4     

Impacted Files	Coverage Δ
...onomy/io/spectral_cube/tests/test_spectral_cube.py	89.18% <84.21%> (+3.47%)	:arrow_up:
glue_astronomy/__init__.py	100.00% <100.00%> (+28.57%)	:arrow_up:
...lue_astronomy/translators/tests/test_spectrum1d.py	100.00% <100.00%> (ø)

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[pllim]

@dhomeier , this PR should be uncontroversial?

[astrofrog]

I'll investigate the CASA failures separately

[pllim]

Whoops, @dhomeier , this PR was already merged.

[dhomeier]

Ah, seems the second pair of eyes was already faster than the first! Should not keep my review tabs open over night!