test(pairs): cover pair-meta validation and info defaults

[changliuchang777]

Summary

• Add pair-meta tests for default /info aggregation on registered pairs.
• Cover fee_bps boundaries, out-of-range/non-integer/array/object rejection, unknown-body-key rejection, and canonical error envelopes.
• Cover min, max, and liquidity invalid string-shape cases, array/object rejection, unregistered 404 envelopes, and default /info metadata.
• Tighten minAmount and liquidity validation to reject leading-zero integer strings while still allowing 0 as the unset value.

Fixes #15

Validation

• git diff --check (passes; only Git for Windows LF/CRLF warnings shown)
• npm install --no-audit --no-fund (passes; npm warns current Node v20.15.0 is below eslint-visitor-keys preferred engine)
• npm test -- --runInBand (blocked by existing baseline: src/index.ts redeclares WEBHOOK_MAX_EVENTS, causing import-time parse failures across suites; unrelated store timestamp assertions also fail)
• npm run build (blocked by existing baseline TypeScript errors: duplicate declarations in src/index.ts, missing/extra PairMeta fields, missing BULK_ABSOLUTE_MAX, undefined quote variables)
• npm run lint (blocked by existing baseline lint errors in existing files, including errorHandler.test.ts, securityHeaders.test.ts, and unused declarations in src/index.ts)