spectrum1d importer to support spectrum list/concatenate

[kecnry]

Description

This pull request absorbs the functionality of 1D Spectrum List and 1D Spectrum List Concatenated into 1D Spectrum and generalizes the underlying code.

TODO:

• fix hash support
• remove/deprecation spectrumlist/concatenate importer?
• fix concatenation support and ensure test coverage exists
• ensure WFSS coverage is still in tests
• fix prefix/not-prefix support for data-label (keeping in mind future plan to add source into default data-label)
• follow-up: extension select API to clear selection (when to expose this?) with API hint

[rosteen]

I didn't turn up any bugs in testing, and didn't see anything I object to from a quick look at the code. Seems good to me.

[rosteen]

This is the intermittent Specviz2D failure right, not related?

FAILED ../../.tox/py311-test-alldeps-cov/lib/python3.11/site-packages/jdaviz/configs/specviz2d/tests/test_parsers.py::test_2d_parser_ext_hdulist - ValueError: ('no valid loaders found for input, tried', {'file': "resolver exception: 'https://stsci.box.com/shared/static/l1dmioxuvtzyuq1p7o9wvjq8pph2yqkk.fits' is not a valid file path.", 'url': "resolver exception: You requested to cache data to the `local_path`='/home/runner/work/jdaviz/jdaviz/.tmp/py311-test-alldeps-cov/.'. This keyword argument is supported for downloads of MAST URIs via astroquery, but since the remote file at 'https://stsci.box.com/shared/static/l1dmioxuvtzyuq1p7o9wvjq8pph2yqkk.fits' will be downloaded using `astropy.utils.data.download_file`, the file will be stored in the astropy download cache instead.", 'object': 'not valid', 'astroquery': 'resolver exception: Resolver subclass must implement default_input', 'virtual observatory': 'resolver exception: Resolver subclass must implement default_input'})