feat: add end-to-end REST API v2 test suite (DIS-71)

- Covers all REST API v2 endpoint families: collections, NFTs, listings,
  offers, events, accounts, tokens, search, swap quote, fulfillment data
- Zod schema validation for all response types
- Pagination (cursor-based) verification
- Error handling tests (404s, invalid inputs, missing API key)
- Latency benchmarking and response size measurement
- Rate-limit and Cache-Control header checks
- JSON report output to test-reports/rest-api-e2e-report.json
- Gated by LIVE_TEST=true environment variable for CI

Co-Authored-By: Chris K <ckorhonen@gmail.com>

Author: devin-ai-integration[bot]