Improve handling of revert button enabled state

[mwcraig]

This PR fixes a mistake I think made in #310. in handling whether the save and revert buttons in the button bar were enabled.

In that PR I made it so that the save and revert buttons were enabled only if:

• there were unsaved changes AND
• the widget held a valid pydanitc model.

That makes sense for the save button -- you should only be able to save a valid model.

Requiring the widget hold a valid pydantic for the revert button makes little sense. One of the reasons you might want to revert, after all, is that you have accidentally entered one or more invalid fields.

This PR changes the behavior for the revert button so that it is enabled whenever there are unsaved changes.

@JuanCab and @Tanner728 -- a look at the code would be great, but confirmation that this new logic makes sense would be enough...I'm reasonably confident the code does what it should.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.86%. Comparing base (e0155c0) to head (d901d65).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #314      +/-   ##
==========================================
+ Coverage   73.80%   73.86%   +0.05%     
==========================================
  Files          27       27              
  Lines        3402     3409       +7     
==========================================
+ Hits         2511     2518       +7     
  Misses        891      891              

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[Tanner728]

All of the code looks good to me, although I don't have much experience with UI stuff. I did some quick testing of it and all of it seems to work as expected. I know we had talked about the revert button earlier but have forgotten what you had decided to do with it as it still does nothing. Just to let you know.

[mwcraig]

it still does nothing. Just to let you know.

A PR to fix that is coming, but I needed to address enabling the revert button first (and am trying to keep the PRs smaller and easier to review)

[JuanCab]

The code looks good. I also looked at the notebook, specifically:

I executed the following commands:

conda create -n test-314 python=3.11 astroscrappy
conda activate test-314
pip install git+https://github.com/mwcraig/stellarphot.git@improve-default-revert-enabled

and then tried the saveable-settings.ipynb notebook. It behaved as advertised (as far as I could tell through creating one entry and then changing it).