Address the review findings on the BEAM parser:
- Cap export, import, and lambda rows at 65536 combined, checked
before any row is allocated.
- Reject any form remainder shorter than a chunk header, including
zero-filled ones.
- Reject AtU8 atom names that are not valid UTF-8 instead of
replacing bytes.
- Read the OTP 28+ compact AtU8 layout (negated count, compact
u-tag name lengths), which was rejected as over the atom budget.
- Add a compiler-produced OTP 29 BEAM fixture whose expected atoms,
table rows, and Code header come from beam_lib on the same file.