Compile-time edge module compilation check, native support for ConstMapObserver

[rmalmain]

follow-up of the patches i introduced in #2520 on edge module. it improves how map_observer guarantees are done at compile-time when building an edge module, with a nicer error message in case the right function is not called.

[domenukk]

the trait `Deserialize<'_>` is not implemented for `[T; N]`, which is required by `OwnedMutSizedSliceInner<'_, T, N>: Deserialize<'_>`

[domenukk]

Status?

[domenukk]

You can try if the nonnull!() macro works for pointers as well. It should as long as it can be evaluated in the const context

[rmalmain]

good to go @domenukk or is there something else to discuss?

[domenukk]

Feel free to merge after cargo fmt, this is good to go.