stdlib_mix_backup_pre_squash: test(stdlib): extend Bounded/UnsignedAbs coverage to all integer types

The original fixtures spot-checked i8/i32/i256 (and u8/u32/u256 for Bounded) on the assumption that the per-type impls were mechanical copy-paste. Adding the remaining types (u16, u64, u128, usize, i16, i64, i128, isize) so that any typo in the per-type literals — wrong type name, wrong constant — would fail loudly. For Bounded: each type asserts both T::min() and T::max() . For UnsignedAbs: each…