least_block_t<N> is the narrowest fixed-width block holding N bits in one: uint8_t where N <= 8, uint16_t
where N <= 16, uint32_t where N <= 32, and uint64_t otherwise, of which N bits then take several.
least_block_t<0> is uint8_t.
bit_least<Owner>:
Constraints:remove_cv_t<Owner> is a resizable owner, whose width picks the block.
Result:bit_rebind<least_block_t<N>, Owner>, where N is Owner's width.
bit_least<basic_bit_array<uint64_t, 9>> is basic_bit_array<uint16_t, 9>, and bit_least<bit_fixed_set<9>>
is basic_bit_fixed_set<size_t, uint16_t, 9>. bit_set is turned away.
Remarks: The name is <cstdint>'s: uint_least8_t is the smallest type of at least 8 bits. bit_enum_set and
bit_flag_set are bit_least over a fixed set.