[Cross-cutting] Set up comprehensive test infrastructure

[konard]

Summary

This PR sets up comprehensive test infrastructure for both JavaScript and Rust implementations as requested in issue #23.

JavaScript Changes

• Vitest Configuration: Added vitest.config.js and vitest.integration.config.js for coverage reporting alongside existing test-anywhere for multi-runtime support
• Test Fixtures (js/tests/fixtures/):
  • sample-links.js: Sample data including simple links, nested links, BigInt links, queue items
  • generateSequentialLinks() and generateRandomLinks() helper functions
• Test Helpers (js/tests/helpers/):
  • test-utils.js: Utilities like createTestStore(), createPopulatedStore(), retry(), measureTime(), runBenchmark()
  • mock-backend.js: Mock implementations with configurable latency and failure injection
• Integration Setup: tests/integration/setup.js with resource cleanup tracking
• CI Updates: Added coverage job that runs Vitest and uploads coverage artifacts

Rust Changes

• Criterion Benchmarks (rust/benches/):
  • memory_bench.rs: Benchmarks for MemoryLinkStore (create, get, exists, find, count, update, delete, clear)
  • queue_bench.rs: Benchmarks for MemoryQueue (enqueue, dequeue, peek, depth, roundtrip, bulk operations)
• Test Fixtures (rust/tests/fixtures/mod.rs):
  • Sample links and link patterns
  • Bulk data generators (generate_sequential_links(), generate_random_links())
  • Store fixtures for consistent test setup
  • Assertion helpers
• CI Updates: Added bench job that compiles and runs Criterion benchmarks with artifact upload

Test Results

• ✅ JavaScript: 469 tests passing (Node.js, Bun, Deno)
• ✅ Rust: 360 tests passing (Ubuntu, macOS, Windows)
• ✅ Rust benchmarks compile and run successfully
• ✅ All CI checks pass

New Scripts

JavaScript:

• npm run test:coverage - Run tests with Vitest coverage
• npm run test:integration - Run integration tests
• npm run test:watch - Watch mode for development

Rust:

• cargo bench --bench memory_bench - Run memory store benchmarks
• cargo bench --bench queue_bench - Run queue benchmarks

Test Plan

• Run existing JavaScript tests (469 pass)
• Run existing Rust tests (360 pass)
• Verify Rust benchmarks compile
• CI runs coverage job and uploads artifacts
• CI runs benchmark job and uploads results

Fixes #23

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[konard]

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