Remove pattern `std::mdspan<> const ...`

[jamesETsmith]

General

We should remove the pattern std::mdspan<...> const .... For views, the const here doesn't prevent people from modifying the underlying data, just the view itself, which isn't usually a useful restriction.

[stand-by]

I'd suggest to modify our use cases to std::mdspan<const T> where possible. This would preserve the constness of elements and provide “read only” access