Reject IVF binary quantizer when dimensions not divisible by 8

The binary quantizer uses D/8 for buffer sizes and memset, which
truncates for non-multiple-of-8 dimensions, causing OOB writes.
Rather than using ceiling division, enforce the constraint at
table creation time with a clear parse error.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>