Add tranche-based parallel itests and enable in CI

[ffranr]

• Add tranche splitting/shuffling support to itest harness and wire per-tranche logging/exit reporting.
• Introduce itest_parallel runner/Make targets (with and without backward-compat binaries) and per-tranche log directories.
• Update GitHub Actions itest matrix to use parallel tranches (4).

[gemini-code-assist]

Summary of Changes

Hello @ffranr, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the efficiency of the integration test suite by enabling parallel execution. It introduces a robust system for dividing tests into manageable tranches, shuffling them for even distribution, and providing isolated logging for each parallel run. This change is crucial for reducing CI build times and accelerating developer feedback cycles, ultimately improving the development workflow.

Highlights

• Parallel Integration Tests: Introduced the capability to run integration tests in parallel by splitting them into 'tranches'.
• Tranche Splitting and Shuffling: The integration test harness now supports dividing the test suite into tranches and deterministically shuffling test cases to balance workload.
• Dedicated Logging and Reporting: Implemented per-tranche logging and exit reporting to provide clear feedback on the status of each parallel test run.
• New Make Targets: Added itest-parallel and itest-parallel-no-backward-compat Make targets to easily trigger parallel integration test execution.
• CI Integration: Updated GitHub Actions CI matrix to leverage the new parallel tranche functionality, initially configured for 4 tranches.

Ignored Files

• Ignored by pattern: .github/workflows/** (1)
  • .github/workflows/main.yml

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[gemini-code-assist]

Code Review

This pull request introduces parallel execution for integration tests by splitting them into tranches. The changes include new Makefile targets, shell scripts for orchestration, and modifications to the Go test runner to support test splitting and shuffling. Overall, the implementation is solid and well-structured. I have one suggestion in itest/litd_test.go to improve the random number generation by using the standard math/rand package and avoiding seeding the global random number generator, which is a recommended practice for robustness and test isolation.

[ffranr]

I think branch protection rules need to be updated for CI to pass.