Add WebSocket order book delta validation tests (#4)

[fengyangxxx]

Summary

Adds deterministic WebSocket/order book delta validation coverage for #4. The change introduces focused order book delta helpers plus parser tests for WebSocket delta payloads, covering malformed payloads, stale/out-of-order sequences, checksum mismatch state preservation, and a valid snapshot-to-delta update path without live services.

Changes

• Added orderbook.SnapshotUpdate / orderbook.DeltaUpdate helpers for deterministic snapshot and delta application.
• Added validation for symbol, side, price, quantity, previous/current sequence ordering, empty deltas, and checksum mismatch.
• Added WebSocket delta payload parsing for bid/ask array payloads and side-tagged change payloads.
• Added deterministic tests in market/orderbook, market/matching, and market/ws.
• Added root go.work so the required repository-root command go test ./market/orderbook ./market/matching ./market/ws runs against the existing market module.
• Included the script-generated diagnostic pair for code commit c0ddfd5c:
  • diagnostic/build-c0ddfd5c.json
  • diagnostic/build-c0ddfd5c.logd

Testing

• go test ./market/orderbook ./market/matching ./market/ws - pass
• python3 build.py in Linux Docker build environment - generated the committed diagnostic pair
  • total modules: 10
  • passed: 7
  • failed: 3 unrelated existing environment/module failures
  • market: PASS
  • unrelated failures: frailbox, engine, openapi-haskell
• python -m json.tool diagnostic/build-c0ddfd5c.json - pass

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

---

• I would like to request that my diagnostic build log is removed before merging

Closes #4