The interface for commit data generation should be reworked

[mationorato]

Discussion: matter-labs#1015 (comment)

Current implementation spreads across multiple crates and has arguably unexpected design decisions (e.g. structures that were POD before now include behavior). The proposal on how to avoid it is shared.

It’s better to fix it before it becomes a problem since the problems with design are pretty hard to solve once the design decision is implemented.