Adds lazy loading + streaming queue population for minitest-queue

[danielahrnsbrak]

Summary

This PR adds lazy loading + streaming queue population for minitest-queue to improve startup behavior and memory profile for large suites, while keeping existing eager mode intact.

What changed

• Added lazy-load execution flow for Minitest:
  • New lazy queue population strategy and on-demand test resolution.
  • Leader streams discovered tests to Redis in batches while non-leaders begin consuming immediately.
• Added new queue entry encoding/parsing (test_id + metadata), and updated Redis Lua scripts to operate on entry payloads safely.
• Added runtime components for lazy mode:
  • ClassResolver
  • FileLoader
  • QueueEntry
  • LazyEntryResolver
  • LazyTestDiscovery
• Extended Redis worker behavior:
  • stream_populate support
  • streaming state management (streaming/ready)
  • stale-stream detection with timeout handling
  • worker profile recording improvements
• Extended CLI/config support:
  • --lazy-load
  • --lazy-load-stream-batch-size
  • --lazy-load-stream-timeout
  • --test-files
  • CI_QUEUE_LAZY_LOAD_TEST_HELPERS
• Documentation updates:
  • Expanded lazy-load docs and usage guidance.
  • Explicitly clarified lazy loading/streaming is currently supported only for minitest-queue (not rspec-queue).

Why

Large test suites pay a high boot cost when every worker eagerly loads all test files.
This change allows:

• faster time-to-first-test for non-leader workers,
• reduced per-worker memory pressure,
• better behavior for very large file lists (--test-files).

Test plan

• bundle exec rake test
• Verified no test failures: 195 tests, 642 assertions, 0 failures, 0 errors, 0 skips
• Verified coverage report generation

Notes

• Lazy loading and streaming are Minitest-only in this PR.
• Existing non-lazy execution path remains supported.