adds `ranges::basic_unformatted_istream_view`

[cjdb]

istream_view is only useful if the input to be formatted on read and std::istreambuf_iterator only works with types that have a std::char_traits specialisation.

The purpose of unformatted_istream_view is to read from an istream object without formatting (so integers will be read as binary rather than as text).

[cjdb]

A brief look at the failed builds suggests this is related to #1587.