use correct spectral density equivalencies for marker unit changes

[gibsongreen]

Description

This pull request is to address updating the spectral density equivalencies to use the original spectral axis so plugin Markers update to the correct position on the spectrum after a unit change.

Original Behavior:

Untitled3.mov

Updated Behavior:

Untitled.2.mov

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. Bugfix milestone also needs an accompanying backport label.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[pllim]

Thanks. Is it possible to add regression test that fails on main but passes here?

[cshanahan1]

(i think this will be fixed by my related ticket btw)

[pllim]

i think this will be fixed by my related ticket btw

Does that mean this PR is a duplicate and unnecessary?

[cshanahan1]

yes but i think its fine as a patch

[pllim]

@cshanahan1 , so is your plan to revert this in your PR, or undo your patch over there?

[cshanahan1]

@cshanahan1 , so is your plan to revert this in your PR, or undo your patch over there?

it will just be a one line swap, and test coverage

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.56%. Comparing base (56e1ded) to head (9d67b5d).
Report is 116 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3219   +/-   ##
=======================================
  Coverage   88.56%   88.56%           
=======================================
  Files         125      125           
  Lines       18755    18755           
=======================================
  Hits        16610    16610           
  Misses       2145     2145           

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[gibsongreen]

Thanks. Is it possible to add regression test that fails on main but passes here?

I added some test coverage that addresess changes to the flux unit. I wrote additional coverage for translations in Cubeviz that I think should go in a small follow up after @cshanahan1 PR.

This is the test on main with the example notebook and the values for the spectrum slice flux and the marker flux:

[pllim]

Thanks!