Update Channel Master UI logic for slider sync behaviour.

[JaschaW]

Description of Changes

Updated the Channel Master UI logic to correctly handle slider synchronisation when multiple rows are selected. The previous implementation propagated values inconsistently when editing a single slider. The new logic ensures that only selected rows update together and solo edits behave correctly. This improves usability and fixes incorrect update behavior in the Channel Master tool.

Testing Done

Manually verified slider behavior when:

• Editing a slider with multiple rows selected.
• Editing a slider when only one row is selected.
• Editing a slider that is not part of the current selection.
• Confirmed that solo edits no longer propagate to unselected rows.
• Confirmed that multi-selection edits update only the intended sliders.
• No errors or unexpected UI updates observed during testing.

Related Issue(s)

#539