feat: add 'obs' group with ra/dec, layout keys to uvh5 files

[aknierim]

just a small PR to add ra/dec (and also the layout name) to comply with new ra/dec requirements in the Gridder class of pyvisgrid

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.47%. Comparing base (3186afd) to head (3f3c00e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #154   +/-   ##
=======================================
  Coverage   99.47%   99.47%           
=======================================
  Files          29       29           
  Lines        1887     1891    +4     
=======================================
+ Hits         1877     1881    +4     
  Misses         10       10           

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