redshift slider select wide enough to avoid overflow

[kecnry]

Description

This pull request fixes a minor annoyance in the width of the select element (between redshift and RV) in the specviz redshift slider. See before and after screenshots below.

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 change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #989 (a94ab1b) into main (ef350a4) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #989      +/-   ##
==========================================
- Coverage   70.64%   70.53%   -0.12%     
==========================================
  Files          74       74              
  Lines        5437     5437              
==========================================
- Hits         3841     3835       -6     
- Misses       1596     1602       +6     

Impacted Files	Coverage Δ
...configs/default/plugins/data_tools/file_chooser.py	65.71% <0.00%> (-3.43%)	⬇️

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[rosteen]

Nice. Somehow I never thought to change this despite it bugging me.

[pllim]

Is fixing RV value getting cut off in scope here or not? This screenshot was taken using this PR branch.

[kecnry]

Updated the PR to also set a min-width on the text input with room for 6 digits (and while I was at it, I fixed the text-input to not crash when putting in non-numeric characters). We may want to consider a dynamic width at some point, but that proved to be a bit tricky to avoid jittering and encroaching on the space of the slider itself.

[pllim]

Let's get this in. Thanks!