By working with binary numbers as integers rather than byte strings, we
don't need to allocate a Vec for each of them, reducing us to just the
allocations in the outer Vec.
Simplify part 2 a lot, by not actually computing the sums because they
do not matter, only the changes do. Also eliminate the allocation
overhead while parsing line-by-line input.
Fixes the existing clippy error because the offending line no longer
exists.
