Fix specviz2d model fit linking

[pllim]

Description

This pull request is to fix modeling fitting linking in Specviz2D so that fitted model does not appear weird over x=0 and would instead plot properly on 1D spectrum viewer. We do not support 2D model fit, so it will never have to display in 2D spectrum viewer.

With this patch:

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]

Without this patch, this test would fail on main as such:

>       assert elink.data1.label == "Spectrum 1D" and elink.data2.label == "model", (elink.data1.label, elink.data2.label)  # noqa: E501
E       AssertionError: ('Spectrum 2D', 'model')
E       assert ('Spectrum 2D' == 'Spectrum 1D'
E
E         - Spectrum 1D
E         ?          ^
E         + Spectrum 2D
E         ?          ^)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.53%. Comparing base (2ed942d) to head (ab36fe0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3434   +/-   ##
=======================================
  Coverage   87.53%   87.53%           
=======================================
  Files         128      128           
  Lines       19962    19962           
=======================================
  Hits        17474    17474           
  Misses       2488     2488           

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