copybook-rdw-predicates

Single-responsibility microcrate for the RDW ASCII-digit header heuristic.

This crate contains the shared byte-level predicate used to quickly detect length-byte corruption patterns in RDW headers. It intentionally stays narrow:

• rdw_is_suspect_ascii_corruption checks whether RDW length bytes look like ASCII digits.
• rdw_is_suspect_ascii_corruption_slice applies the same predicate to a variable-length byte slice with bounds guarding.