unescape_rbsp pushed every byte into the output Vec one at a time. It now
scans for 00 00 03 with the usual skip rule (a nonzero byte at i rules out
a match ending at i + 1 or i + 2, so the scan advances by 3) and copies the
bytes between matches with extend_from_slice. No unsafe, no indexing that
can panic.
Output is identical: a removed 03 still restarts the zero count. Tests
compare it with a verbatim copy of the old function over 20000 random
buffers (fixed-seed PRNG) and list the edge cases (empty input, 00 00 03 at
the end, 00 00 03 03, runs of zeros).
Closes#518
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>