Prepare jamhash 0.1.3 release

[St4NNi]

Description

Prepare jamhash 0.1.3 for release while preserving the established jamhash_u64 mapping and narrowing public claims to the archived evidence.

Changes

• Define and regression-test jamhash_bytes, JamHasher, empty-write, byte-order, and fixed-hasher semantics.
• Document the complete canonical packed k=21 evidence separately from the mutation study and end-to-end screening claims.
• Preserve zero-inclusive archived thresholds and add verified runtime-equivalent zero-excluding counts.
• Add reproducible evidence, package, MSRV, Miri, s390x, tag/version, and publication gates.
• Update GitHub Actions checkout to the supported Node.js 24 release.