feat: implement attestation, XDR encoding, consensus, and wallet throttling

[observerr411]

Summary

Resolves four issues in a single PR.

---

closes #508 — Account attestation & credential management

• Typed AccountAttestation and CredentialMetadata model in the account module
• issueAttestation(subject, credential) with issuer validation and deterministic HMAC-SHA256 payload signing
• verifyAttestation(attestation) for signature, subject, and expiration verification
• revokeAttestation with revocation registry; revoked credentials fail verification even with valid signatures
• Duplicate prevention via per-account issuance registry (same issuer + credential ID rejected)
• getAccountAttestations(account, filters) — query by issuer, type, credential ID, or validity (checks registry for post-storage revocations)
• Structured SorokitError responses for expired, malformed, revoked, or untrusted attestations
• Private credential attributes never exposed through logs or serialized errors
• Exported from src/account/index.ts and src/index.ts
• 24 tests covering issuance, verification, expiration, revocation, duplicate detection, malformed signatures, invalid issuers, and query filtering

---

closes #505 — Transaction XDR encoding for bandwidth efficiency

• Optional DEFLATE compression for large XDR payloads with byte-for-byte round-trip fidelity
• Delta-based encoding for similar transaction structures using prefix-diff representation
• EncodingMetadata identifies the strategy required for decoding (none / deflate / delta)
• Small payloads bypass compression automatically when overhead exceeds savings threshold
• Compression failures fall back safely to standard uncompressed XDR
• Configurable: minCompressionSize, maxCompressionOverhead, compressionLevel, enableDeltaEncoding
• Exported from src/transaction/index.ts and src/index.ts
• 23 tests covering round-trips, corrupted payloads, small payloads, delta encoding, cache management, and config options

---

closes #507 — Threshold-based multi-party transaction consensus

• createConsensusTransaction(threshold, participants) validates threshold ≤ participant count and no duplicate IDs
• Independent tracking of approvals, rejections, and pending participants per consensus workflow
• States: proposal → review → approved / rejected → finalized
• Duplicate approvals/rejections from the same participant are rejected with structured errors
• finalizeConsensusTransaction is blocked until threshold is met and no rejections exist
• Consensus state is kept separate from the underlying transaction object — no silent submission
• Exported from src/transaction/index.ts and src/index.ts
• 26 tests covering threshold success, rejection, duplicates, invalid config, and full workflow

---

closes #506 — Wallet connection throttling & abuse detection

• Per-origin rate limiting with configurable attempt window and block duration
• Authentication failure tracking contributes to abuse detection independently of general failures
• Excessive requests trigger temporary backoff; blocked requests return structured errors with retryAfterMs
• Allowlist and blocklist rules with optional expiration (no restart required)
• detectAbuse(origin) scores confidence across patterns: rapid attempts, repeated failures, auth failures, high failure rate
• Existing wallet integrations unaffected when enabled: false
• Exported from src/wallet/index.ts and src/index.ts
• 39 tests covering normal retries, bursts, auth failures, allowlists, blocklists, expiry, and structured errors

---

Test results

✓ src/wallet/throttling.test.ts       39 tests
✓ src/account/attestation.test.ts     24 tests
✓ src/transaction/consensus.test.ts   26 tests
✓ src/transaction/xdrEncoding.test.ts 23 tests

Test Files  4 passed (4)
Tests       112 passed (112)

[drips-wave]

@observerr411 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits