Create Interfaces Using mdspan and accessors for heterogeneous memory

[Fuad-HH]

Got the idea from the first half of: https://youtu.be/AbHpRnnpUk0

[jacobmerson]

@Fuad-HH I don't have time to watch the video. How does that approach compare to what we are doing in PCMS? Here:https://github.com/SCOREC/pcms/blob/develop/src/pcms/utility/arrays.h

Are there aspects of our PCMS approach that would benefit from updates?