[2pt] Describe limitations and difference in behaviors of box operations for memtx and vinyl

What needs to be done

Reviewer: @ documentarian name

Right now we have a separate page about engines (memtx and vinyl) where differences and limitations are described. However, pages that describe box operations don't mention these limitations and differences. For example box:len() - https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/len/
I propose to fix it.

Definition of done

• pages about box:alter(), box:random(), box:len(), box:count() and box:delete() describes a difference in behaviour for memx and vinyl engines OR contains a link to a page where these differences described.

Start with the existing engines page covering memtx and vinyl, then review the documentation pages for box:alter(), box:random(), box:len(), box:count(), and box:delete(). Compare their current descriptions with the engine differences and limitations, and consider the box:len() page as the example entry point. Done means each page describes the engine-specific behavior or links to a page that does.