fix(encoding): validate block bitpacking payloads

[Xuanwo]

Stack 5 of 10 for Lance generic block sequence compression.

Block bitpacking previously trusted header-derived widths and payload lengths too far into decompression. This makes the codec reject invalid bit widths, misaligned chunks, inconsistent value counts, and truncated or oversized payloads before unpacking, including the valid zero-width case.

Valid persisted bytes are unchanged; the user-visible difference is that malformed data returns a bounded corruption error instead of reaching unchecked decode assumptions.

Stack navigation

• Position: 5 of 10
• Root: refactor(encoding): align block codecs with miniblock #8324
• Previous: feat(encoding): compose generic block codecs #8327
• Next: fix(encoding): bound general block decompression #8329
• Top: perf(encoding): measure compressed mini-block offsets #8333