A procedural macro fully implementing [IterableByValue] and
[IterableByValueFrom] for subslices on top of a the SubsliceImpl
structure generated by the derive macro [Subslice].
A procedural macro fully implementing [IterableByValue] and
[IterableByValueFrom] for subslices on top of a the SubsliceImplMut
structure generated by the derive macro [SubsliceMut].
A procedural macro fully implementing mutable subslices on top of a
[SliceByValueSet]/[SliceByValueRepl] for which the derive macro
[Subslice] has been already applied.