Fixed return type and shape for pixel <-> world conversions in SpectralCoordinates

[astrofrog]

The pixel <-> world methods should return single scalars/arrays not tuples in order to be APE-14-compliant.

[pllim]

Is it a concern that the CI fails here?

[codecov]

Codecov Report

Base: 96.99% // Head: 97.12% // Increases project coverage by +0.13% 🎉

Coverage data is based on head (7be8779) compared to base (8d2a3e4).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
+ Coverage   96.99%   97.12%   +0.13%     
==========================================
  Files          17       18       +1     
  Lines        1296     1324      +28     
==========================================
+ Hits         1257     1286      +29     
+ Misses         39       38       -1     

Impacted Files	Coverage Δ
...lue_astronomy/translators/tests/test_spectrum1d.py	100.00% <ø> (ø)
glue_astronomy/spectral_coordinates.py	100.00% <100.00%> (+6.66%)	⬆️
glue_astronomy/tests/test_spectral_coordinates.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[pllim]

I tried this out at spacetelescope/jdaviz#1968 but now it fails with an even more obscure error:

AttributeError: 'numpy._ArrayFunctionDispatcher' object has no attribute '__code__'

https://github.com/spacetelescope/jdaviz/actions/runs/3959079839/jobs/6781436962

[dhomeier]

spectrum1d test was still expecting the old, incorrect shape.

[pllim]

Oh wait... glue-astronomy==0.5.1 ... I think I have to remove pin because I am trying to install it from fork branch that has no tags. Hold on.

[dhomeier]

Fixes the jdaviz test suite for me (macos-py310), but should probably wait for @pllim's test PR to at least run.

[pllim]

I think this fixes the devdeps job in Jdaviz. Thanks!