Archive and compare iterations.log for implicit coupling

[PranjalManhgaye]

Summary

Implicit coupling tutorials write precice-*-iterations.log files that show how many coupling iterations each time step needed. This PR adds system-test support to save those logs and check them against reference copies, so we notice when coupling behaviour changes unexpectedly. Closes #440.

Changes

• Systemtest.py: After a tutorial run, collect precice-*-iterations.log files into iterations-logs/ and compare them by SHA-256 hash against archived reference copies in a *.iterations-logs/ directory next to each reference .tar.gz. A successful check is logged at INFO; a mismatch fails the test.
• generate_reference_results.py: When you regenerate reference results, the iterations logs are copied into that *.iterations-logs/ folder so future runs have something to compare against.
• README.md: Documents the behaviour.
• changelog-entries/743.md: Changelog entry for this PR.

test (local)

Notes

• Tests without reference iterations logs skip comparison (unchanged tutorials).
• Explicit coupling (no iterations logs) is unaffected.

Checklist

• Changelog entry in changelog-entries/743.md

[precice-bot]

This pull request has been mentioned on preCICE Forum on Discourse. There might be relevant details there:

https://precice.discourse.group/t/gsoc-2026-pranjal-manhgaye/2769/5

[MakisH]

@PranjalManhgaye could you please resolve the merge conflicts and prepare this PR for reviewing?

[MakisH]

Some first comments. I have not yet looked at the complete PR or tested it.

[PranjalManhgaye]

thanks @MakisH for your review , i will make this pr review ready and also resolve conflicts .

[PranjalManhgaye]

Hi @MakisH , rebased onto develop, updated the PR description, and replied on your review threads. ready for another look when you have time.

[MakisH]

I have not yet completed my review, but here is already a first comment on something to check.

Tests I have executed locally:

• python3 systemtests.py --suites="openfoam_adapter_release" (no iterations in the reference results) succeeds
• python3 generate_reference_results.py --suites="openfoam_adapter_release" worked and generated results in an (uncompressed) folder flow-over-heated-plate/reference-results/fluid-openfoam_solid-openfoam.iterations-logs with fluid-openfoam/precice-Fluid-iterations.log and solid-openfoam/precice-Solid-iterations.log.
• after updating the reference results: python3 systemtests.py --suites="openfoam_adapter_release" worked, but I don't see sha256 or iterations in the output to confirm.

[PranjalManhgaye]

Hi @MakisH , pushed 095502d ; removed the JSON sidecar fallback and added INFO output when the iterations hash check passes.
Re-tested openfoam_adapter_release locally => same steps as you, and the second run now shows the INFO line.readme updated ,
Ready for another look when you can.