Follow-up Number tasks

[johnmcfarlane]

• Documentation
• cnl::_impl::native_tag -> cnl::native_tag
• cnl::_impl::multiply_op -> cnl::multiply_op etc.
• remove operators with tags from different tag families, e.g. convert<native_tag, nearest_rounding_tag, int>
• investigate replacement of cnl::from_value with a single cnl::_impl::deduce which uses specializations of cnl::deduction to perform the simple conversion all of the from_value specializations seem to do.
• assert_same -> assert_same_v