Fix #27291: Prevent tuplet item being merged when regrouping rests

[lokanchung]

Resolves: #27291

Currently when merging rests, regroup rhythm does not consider tuplets. However, current logic won't check if next rest has tuplet or not. Merging non-tuplet rests and tuplet rests eventually removes the tuplet and end up with removing existing notes.

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[zacjansheski]

Tested on MacOS Tahoe 26.2, Windows 11, Ubuntu 22.04.3. Approved
#27291 FIXED