per-config display of unit selections

[kecnry]

Description

This pull request provides the infrastructure for configs (and downstream apps) to dictate which display units should be shown in the plugin, as well as including a time unit (currently unused for all configs, but needed by lcviz). The individual logic may need to be adjusted as unit conversion is enabled for the remaining configs (I just made a rough guess). This PR also makes the surface-brightness API access read-only.

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)?

[codecov]

Codecov Report

Attention: Patch coverage is 96.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.41%. Comparing base (cd70c2e) to head (c43f450).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...specviz/plugins/unit_conversion/unit_conversion.py	96.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3166   +/-   ##
=======================================
  Coverage   88.40%   88.41%           
=======================================
  Files         124      124           
  Lines       18349    18373   +24     
=======================================
+ Hits        16221    16244   +23     
- Misses       2128     2129    +1     

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[rosteen]

I just pulled this, and the Unit Conversion plugin doesn't render in Cubeviz (it appears in Specviz as expected).

[kecnry]

ah, that was a missed update in the rebase, should be fixed now (sorry about that!)

[rosteen]

I think you missed this string in the rebase, unless you meant to change it back from the more general language.

[kecnry]

nope, missed that too 🤦 Reverted to "Spectral y-axis Type"

[rosteen]

Looks good to me now, thanks.

[pllim]

Suggested change

	self.has_sb = self.has_angle or self.config in ('imviz',)
	self._has_sb = self.has_angle or self.config in ('imviz',)

As per "convention," should this be "hidden" then if read only?

[kecnry]

Traitlets cannot have leading underscores, and this is not exposed to the user

[pllim]

Looks much cleaner code-wise. Thanks! Just a minor question, so approving. Merge at will.