- basic functionality similar to std::span (C++20).
Holds pointer and size: for lightweight handling of address ranges.
- implements cdata_bytes() and data_bytes() methods for similarity
with UList. For span, however, both container accesses are const
but the data_bytes() method is only available when the
underlying pointer is non-const.
No specializations of std::as_bytes() or std::as_writeable_bytes()
as free functions, since std::byte etc are not available anyhow.
