Replace load_spectrum with load_data

[duytnguyendtn]

Description

This pull request brings specviz in line with the other viz tools by deprecating specviz.load_data and replacing it with specviz.load_data. I think I got all the documentation changes as well here. Should be pretty uncontroversial, as we've been asking for this for a long time

The decreased coverage is due to the deprecated method

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Patch coverage: 98.18% and project coverage change: -0.03 ⚠️

Comparison is base (b6feaa6) 91.34% compared to head (a569123) 91.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2273      +/-   ##
==========================================
- Coverage   91.34%   91.32%   -0.03%     
==========================================
  Files         150      150              
  Lines       16848    16849       +1     
==========================================
- Hits        15390    15387       -3     
- Misses       1458     1462       +4     

Impacted Files	Coverage Δ
jdaviz/configs/specviz/helper.py	77.16% <75.00%> (-0.26%)	⬇️
...efault/plugins/line_lists/tests/test_line_lists.py	100.00% <100.00%> (ø)
...default/plugins/model_fitting/tests/test_plugin.py	99.52% <100.00%> (ø)
.../plugins/subset_plugin/tests/test_subset_plugin.py	100.00% <100.00%> (ø)
.../plugins/line_analysis/tests/test_line_analysis.py	99.62% <100.00%> (ø)
...ecviz/plugins/line_analysis/tests/test_lineflux.py	100.00% <100.00%> (ø)
...gins/unit_conversion/tests/test_unit_conversion.py	96.92% <100.00%> (ø)
jdaviz/configs/specviz/tests/test_helper.py	100.00% <100.00%> (ø)
jdaviz/core/data_formats.py	78.37% <100.00%> (+0.50%)	⬆️

... and 1 file with indirect coverage changes

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[pllim]

devdeps failure is unrelated. LGTM but I will refrain from approving until we have that change log because I don't want this to get accidentally merged without one. Thanks!

[pllim]

Isn't it a little too late the improve load_spectrum doc now? 😆 Doesn't hurt though...

[pllim]

LGTM now. Thanks!

[kecnry]

Finally!!!! Thanks!

[duytnguyendtn]

Thanks for the reviews! Merging