feat: Balance acceptance CI shards using recorded test timings

[danskmt]

Pull Request Submission Checklist

• Follows CONTRIBUTING guidelines
• Commit messages are release-note ready, emphasizing what was changed, not how.
• Includes detailed description of changes
• Contains risk assessment (Low | Medium | High)
• Highlights breaking API changes (if applicable)
• Links to automated tests covering new functionality
• Includes manual testing instructions (if necessary)
• Updates relevant GitBook documentation (PR link: ___)
• Includes product update to be announced in the next stable release notes

What does this PR do?

Replaces Jest’s default count/alphabetical --shard split with a timing-aware sequencer so parallel acceptance jobs finish closer together. Adds test-timings.json (per-file weights from CI) and wires it via --testSequencer on test:acceptance. Enables jest-junit addFileAttribute for future timing refreshes.

Where should the reviewer start?

• test/jest/timingSequencer.js — LPT bin-packing in shard()
• test/jest/test-timings.json — recorded acceptance runtimes (ms)
• package.json — test:acceptance sequencer flag and addFileAttribute

How should this be manually tested?

1. Run npx jest --testPathPattern timingSequencer.spec.ts if the unit test is included in a follow-up.
2. Trigger Windows acceptance CI (8 shards) and compare parallel run wall times vs main (expect smaller spread between fastest/slowest shard).

What's the product update that needs to be communicated to CLI users?

None. CI-only change; no CLI behavior change for end users.

Risk assessment (Low | Medium | High)?

Low

Any background context you want to provide?

Jest’s built-in sharding splits by file count, so one shard can pick up slow specs (e.g. snyk-code user journey ~7 min) while others finish much earlier. The custom sequencer assigns each file to the lightest shard by estimated runtime.

What are the relevant tickets?

CLI-1482

Screenshots (if appropriate)

N/A

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