Freeze private callable ABI3 metadata

[wsdt]

What changed

• add the private metadata-only SPXNABI3 compiler encoder
• add an independently implemented native-host parser and canonical re-encoder
• bind the bounded settlement graph and trace-evidence witnesses without reusing v2/proof codecs
• distinguish iOS device, simulator, and Mac Catalyst target identities
• reject canonical and malformed ABI3 metadata in both existing loaders before path/image/symbol access
• document the exact private descriptor contract and preserve runtime/provider/mobile/public nonclaims

Why

This advances RFC 0004 toward physical native ownership recovery while keeping SPX-B104 closed until complete runtime codecs, exact-instance settlement authority, finalizers, mobile evidence, and public admission are proven.

Validation

• 259 core tests
• 87 native-host tests
• all 14 authoritative corpus cases parsed and canonically re-encoded by the independent host
• every-prefix, trailing-byte, single-byte mutation, resealed trace-witness, cross-binding, target, and v1/v2/proof/v3 confusion gates
• loader absent-path and Unix side-effect rejection tests
• strict workspace/all-target/all-feature Clippy
• formatting, doctests, rustdoc, release build, documentation links, examples, and diff checks
• independent review completed with no blockers

The local cargo package network step was unavailable in the sandbox; hosted CI is expected to provide the networked package and cross-platform evidence.