Panning Navigator is very slow

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. With a big score open, open the Navigator
2. Scroll sideways past the edge of the score visible in the Navigator.

Result: the framerate while scrolling instantly plummets. Panning back into the area already loaded into the Navigator is fast again.

Closing Navigator makes scrolling fast through the whole score.

Supporting files, videos and screenshots

https://github.com/user-attachments/assets/540e1cac-0b43-48ca-b61b-44587b6a3518

(Sorry, it's hard to demonstrate the issue well and stay under the upload file size limits.)

In which versions of MuseScore Studio is this issue present?

OS: macOS Sequoia (15.7.7), Arch.: arm64, MuseScore Studio version (64-bit): 4.7.5-260831071, revision: github-musescore-musescore-3654226

Regression

I was unable to check

Operating system

macOS

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

Start by reproducing the issue from the Navigator with a large score, scrolling sideways beyond the area already loaded. Trace the Navigator's panning and score-loading entry points while monitoring framerate on macOS. Done means scrolling remains responsive across the whole score with the Navigator open.