BeatPreview for Pattern Clip causes lag

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System Information

Windows 11; i5 12400; 64 GB RAM

LMMS Version(s)

master, Version 1.3.0-alpha.1.937+13ea2ee (win32/x86_64, Qt 5.15.6, GCC 13-win32).

Most Recent Working Version

Version 1.3.0-alpha.1.900+dc2a461 (unknown platform/unknown processor, Qt 5.15.6, GCC 13-win32).

Bug Summary

#7559 introduces a beat preview to the pattern clip view in song editor.
After this, when the pattern in song editor has several dozens of tracks then scrolling and zooming in the song editor lag extremely even though the rendered view is just a white block.

I cannot claim it is certainly caused by this issue because the latest nightly I have without the issue was from November (the feature was merged in December) and it could be anything between that and my reference nightly (downloaded in January)

Expected Behaviour

When there are hundreds of overall notes or several dozens of active and filled tracks with enough notes (not if there are 30 tracks but only one has notes at all) then do not render preview / show only block without wasting resources calculating.

Steps To Reproduce

Open attached file in LMMS master build vs a build before #7559.

Logs

No response

Screenshots / Minimum Reproducible Project

Screen.Recording.2026-05-20.020104.mp4

I know the build that shows the bug in this video is relatively recent, but I checked the bug against my Version 1.3.0-alpha.1.937+13ea2ee (win32/x86_64, Qt 5.15.6, GCC 13-win32). (has bug)
the build without bug is Version 1.3.0-alpha.1.900+dc2a461 (unknown platform/unknown processor, Qt 5.15.6, GCC 13-win32).

File used:

lb302-torture.zip

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