spectral_frame_conversion domain function

[Jan-Willem]

• Add the function convert_spectral_frame to src/astroviper/_domain/_visibility.
• The function should take in a single ms_xds and return an ms_xds where the Spectral reference frame has been converted to the specified output_reference_frame:
  • convert_spectral_reference_frame(ms_xds, output_reference_frame, ...)
• Astropy should be used for the conversion.
• NumPy docstring should be included.
• Tests should be added to tests/domain/visibility.
• Code should be formatted using Black.