multi_buffer: Refactor diff_transforms field into a separate struct (#32237)

A minor refactor ~needed to unblock #22546; it's pretty hard to add an
extra field to `diff_transforms` dimension, as it is a 2-tuple (which
uses a blanket impl)

Release Notes:

- N/A
7afee64119Piotr Osiewicz committed on 6/6/2025, 11:06:42 AM· committed by GitHubparentcd0ef4b
1 file changedLine totals unavailable