Claim #31 — Verification of <byteorder_lite::BigEndian as byteorder_lite::ByteOrder>::read_u24 (with Aeneas be86ab0f1989d04944292b345b24c435be3ad10a)

This covers 36 selected writer methods, sixteen scoped integer readers, ten native-target identity conversions, and two handwritten Default methods, not all public APIs. Fixed-width 16/32/64/128-bit reads, other bulk and in-place conversions, I/O extensions, other targets and release extraction remain unproved. The float result establishes bit serialization only: floating arithmetic, comparisons, rounding, numeric accuracy, NaN arithmetic and signaling behavior are not modeled. Kani public-writer buffer lengths are fixed at 6 and 10; arbitrary valid slice lengths are quantified separately by the Lean theorems. The write_int documentation says nonrepresentable values panic, while original-body theorems establish truncation for all i64 inputs when count/space guards hold; 176 finite native observations corroborate selected boundaries. This is a documentation/behavior mismatch, not a memory-safety finding. write_i24 documents only short-buffer panic and is not classified as a documentation problem. Other signed reads remain unproved. Opposite-endian conversion methods and other target configurations are not covered by the identity results. Panic messages and unwinding side effects are not specified. Separately, write_int128 documentation also says a nonrepresentable value panics; the original-body Lean theorem establishes truncation for all i128 inputs under valid count/space guards. This additional documentation contrast follows from the proof and source text, with no new native observation claimed; the176 native observations remain specific to the prior signed64/24 investigation.