ByteBuffer::slice_view() allocates a new ByteBuffer object,
which as a RefPtr and everything.
Nowadays it should probably return a Bytes / Span<u8>, but AES was only
using slice_view() to extract the pointer again. So just add ady a
range check at the top, and do pointer arithmetic to do the same thing
faster.
Reduces time to run `disasm /bin/id` by a bit under 40%,
from ~8.3s to ~5s (min-of-3 runs).
8d3d0054ed