Re-enable exporting cubeviz spectrum viewer

[kecnry]

Description

This pull request re-enables support for exporting the cubeviz spectrum viewer (to png or svg) by temporarily "cleaning" any unicode from the marks (which currently exist for the slice indicator).

The cleaning/restoring part of this PR could be reverted if support for unicode is fixed upstream (likely in bqplot).

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

All modified and coverable lines are covered by tests ✅

Project coverage is 88.91%. Comparing base (a39a0fe) to head (929ec1e).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2825      +/-   ##
==========================================
+ Coverage   88.88%   88.91%   +0.03%     
==========================================
  Files         111      111              
  Lines       16983    16985       +2     
==========================================
+ Hits        15096    15103       +7     
+ Misses       1887     1882       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[rosteen]

Looking at the resulting PNG: "oh, it's that space that was causing problems!?"

[rosteen]

Could we also have restore_marks and only populate the two lists if restore isn't empty, to avoid looping over things we don't need to update in the zip later?

[kecnry]

I'm not sure I follow - do you mean store a copy of the original mark? I'm trying to store/restore as little as possible to minimize memory impacts. I tried to avoid the append, but there can be some copying-referencing issues if we're not careful then.

[rosteen]

Suggested change

	restores.append(restore)
	if restore != {}:
	restores.append(restore)
	restore_marks.append(mark)

Would restore_mark have a copy of the object or a reference to the original in this case? I can never keep track of when python does which, but this would avoid looping over things that don't need to be restored. If memory is an issues it can stay as-is, I honestly don't think this is going to be impactful either way here.

[kecnry]

I suspect this would be more expensive than looping over the empty dictionary, but I'm not sure. We could also track indices, but I'm not sure its worth it either 🤷‍♂️

[rosteen]

As I said, I don't feel strongly about it, I'll just approve.

[haticekaratay]

Export works great! It feels the gap of unsupported Unicode in bqplot. Thanks!