Spectrum1D round-trip test

[eteq]

This PR is currently just a (non-functional) test for round-tripping behavior in Spectrum1D. Meant as a starting point for test-driven development regarding an issue I'm about to create

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 🎉

Comparison is base (755874d) 96.92% compared to head (f806a8c) 96.95%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   96.92%   96.95%   +0.02%     
==========================================
  Files          18       18              
  Lines        1399     1411      +12     
==========================================
+ Hits         1356     1368      +12     
  Misses         43       43              

Impacted Files	Coverage Δ
glue_astronomy/translators/spectrum1d.py	94.73% <100.00%> (+0.07%)	⬆️
...lue_astronomy/translators/tests/test_spectrum1d.py	100.00% <100.00%> (ø)

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[dhomeier]

@eteq I have rebased this and committed my proposed solution from #23 (comment) for an initial implementation.