multi_buffer: Split multi_buffer into more modules (#41033)

There are a of separate APIs in this, partially interleaved making it
difficult to grasp.

Release Notes:

- N/A *or* Added/Fixed/Improved ...
6aaf19f276Lukas Wirth committed on 10/23/2025, 5:57:52 PM· committed by GitHubparentd83ed4e
12 files changedLine totals unavailable