Adding new staff may create redundant local time signature

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

When one staff has a local time signature and then a second one that returns to the global time signature, adding a new staff will copy the second time change into the new staff, even though it's redundant there. Also, because of #31568, this redundant time signature can't be removed.

Steps to reproduce:

1. Create a new score with a 4/4 time signature.
2. Drag a different time signature (e.g. 3/4) onto the staff, holding Ctrl to create a local time signature.
3. Drag the original time signature (4/4) onto the staff at a later measure, holding Ctrl to create a local time signature.
4. Add a new staff to the score (either a new instrument, or a new staff to any existing instrument).

When the new staff is added, it will have a copy of the second 4/4 time signature.

Note: this affects any time signatures that are metrically equivalent to the global time. For example, in the above scenario 3/4 or 6/8 are not duplicated into the new staff, but 4/4 or 2/2 are.

Supporting files, videos and screenshots

https://github.com/user-attachments/assets/f21b1e05-2857-4b4f-aad3-19e34968580b

In which versions of MuseScore Studio is this issue present?

4.6.5, master

Regression

No.

Operating system

Windows 10

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

No source file, test, or entry point is named in the report. Reproduce the issue using the listed steps, then locate the staff-addition handling for local time signatures and verify that metrically equivalent signatures are not copied to the new staff; confirm the result with the provided scenario and related cases such as 3/4 and 6/8.