fix: fix a bug in the CoreConnectedGridPlanWidget when selecting the bound mode

[fdrgsp]

Not sure if this is the best fix but...

To reproduce the current bug:

from pymmcore_plus import CMMCorePlus
from pymmcore_widgets.mda._core_grid import CoreConnectedGridPlanWidget
mmc = CMMCorePlus()
mmc.loadSystemConfiguration()
g = CoreConnectedGridPlanWidget()
g.show()
g.setMode("bounds")

Now manually modify any of the top/bottom/left/right values and then run:

g.value()

In the current version the top/bottom/left/right values are always 0.

I'm not sure how to test this because if we setup the widget top/bottom/left/right values with the setValue() method and then we call the value() the top/bottom/left/right values are correct. The difference is that graphically on the widget we do not see the top/bottom/left/right values added through the setValue().

Screen.Recording.2025-01-26.at.1.37.55.PM.mov

[codecov]

Codecov Report

Attention: Patch coverage is 76.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 90.65%. Comparing base (f104046) to head (4796eb0).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pymmcore_widgets/mda/_xy_bounds.py	60.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #396      +/-   ##
==========================================
- Coverage   90.74%   90.65%   -0.09%     
==========================================
  Files          85       85              
  Lines        9374     9360      -14     
==========================================
- Hits         8506     8485      -21     
- Misses        868      875       +7     

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