Minor CI changes for interop testing

[sqt]

Update CI env to match upstream test env more closely, update documentation, add 'current' zzdds binary to tests (backwards-compatibility interop!)

[greptile-apps]

Greptile Summary

The PR aligns interoperability jobs more closely with the upstream test environment and expands compatibility coverage.

• Moves interop jobs to Ubuntu 24.04 and explicitly configures Python 3.11.4.
• Installs the upstream harness’s complete requirements file.
• Adds the published zzdds binary to the interop matrix for release-versus-current testing.
• Updates coherent-set investigation notes and roadmap documentation.

Confidence Score: 5/5

The PR appears safe to merge because no blocking failure remains in the eligible or outstanding review findings.

No blocking failure remains.

Important Files Changed

Filename	Overview
.github/workflows/ci.yml	Updates the interop runner, Python environment, dependency installation, upstream harness ref, and default implementation matrix; no follow-up-eligible comment can be posted without a specific prior thread.
docs/decisions.md	Documents the coherent-set investigation and attributes the observed failures to a timing-sensitive upstream harness assertion.
docs/implementation_status.md	Replaces the prior open interop-gap note with detailed findings from the coherent-set test campaign.
docs/roadmap.md	Reclassifies the coherent-set failures as an upstream harness issue rather than an open implementation gap.

_{Reviews (2): Last reviewed commit: "bumping zenzen ref to get script changes" | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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