feat: add IWalletStateAttestation requirement type support

[CodySearsOS]

Summary

Adds SDK support for @douglasborthwick-crypto's IWalletStateAttestation predicate type (kind 0x7a111640), proposed in the ERC-8257 forum thread.

This is a third-party predicate for gating tool access based on offchain-signed cross-chain wallet state (e.g., Solana, XRPL, Bitcoin holdings verified via RIP-7212 P-256 signature verification). No spec changes needed — the kind extension model already supports this.

Credit to @douglasborthwick-crypto for proposing this predicate type and providing the reference implementation.

Changes

• access.ts: WALLET_STATE_ATTESTATION_KIND constant (0x7a111640), DecodedWalletStateAttestationRequirement type, decodeRequirement() support
• index.ts: export new constant and type
• inspect.ts: display decoded attestation fields for WalletStateAttestationPredicate
• decode-requirement.test.ts: test coverage for all requirement type decoding
• SKILLS.md: WalletStateAttestation predicate documentation

Notes

• No WalletStateAttestationPredicateClient class added — there is no canonical deployment; each issuer deploys their own
• No contract or spec changes — the kind is a third-party extension per the spec's open namespace