[FEA]: Provide for_each_in_extent to directly linearization/de-linearization multidimensional indices with mdspan

[fbusato]

Is this a duplicate?

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Area

libcu++

Is your feature request related to a problem? Please describe.

Working with mdspan with one-dimension iterators (see llc.c) requires to de-linearization and linearization offsets making the process bug-prone and difficult to read and write

Describe the solution you'd like

Provide for_each_in_extent to allow directly working with multi-dimensional indices

Describe alternatives you've considered

No response

Additional context

No response