systemtests: add heat-exchanger-simplified test suite

[AdityaGupta716]

What this PR does

Adds heat-exchanger-simplified to the system test suites in tools/tests/tests.yaml as both a new standalone suite heat_exchanger_simplified_test and as an entry in the existing release_test suite.

Also fixes several Docker and Ubuntu 24.04 compatibility issues that prevented local system test runs.

Changes

tests.yaml

• Added heat_exchanger_simplified_test standalone suite with case (fluid-top-openfoam, fluid-btm-openfoam, solid-calculix)
• Added heat-exchanger-simplified to release_test so it runs in release CI

Systemtest.py

• Added _get_docker_compose_cmd() to auto-detect docker compose vs docker-compose
• Replaced all 3 hardcoded docker compose --file Popen calls to use the detection helper with -f

Dockerfile (ubuntu_2404)

• Used userdel -r ubuntu before creating precice user, removing the default Ubuntu 24.04 user including its home directory — cleaner fix for the UID/GID 1000 conflict
• Added =master defaults for all six adapter ARGs: OPENFOAM_ADAPTER_REF, PYTHON_BINDINGS_REF, FENICS_ADAPTER_REF, CALCULIX_ADAPTER_REF, SU2_ADAPTER_REF, DEALII_ADAPTER_REF
• Added --tries=3 --retry-connrefused --timeout=30 to wget for both CalculiX and SU2 downloads

components.yaml

• Added PYTHON_BINDINGS_REF to calculix-adapter build args

Verification

• Confirmed heat-exchanger-simplified has a complete metadata.yaml with all required participants and cases
• Verified case names match exactly with metadata.yaml
• Confirmed correct parsing via python3 print_test_suites.py — both heat_exchanger_simplified_test and release_test show the new tutorial
• Ran python3 systemtests.py --suites=heat_exchanger_simplified_test --build_args=TUTORIALS_REF:develop — Docker images build and coupled run completes; fails only at field-comparison due to missing reference archive (expected)

Notes on reference results

Reference results for heat-exchanger-simplified will need to be generated on a Linux machine via CI or generate_reference_results.py. The .gitkeep placeholder has been added to heat-exchanger-simplified/reference-results/.

Checklist

• I added a summary of any user-facing changes in changelog-entries/731.md
• I will remember to squash-and-merge with a useful summary

[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-aditya-gupta/2773/2

[AdityaGupta716]

@MakisH plz review!
While adding the test suite I ran into a few things locally Ubuntu 24.04 has a default ubuntu user with UID/GID 1000 which breaks the container build, the Systemtest dataclass was referencing self.timeout without ever declaring the field (would crash with AttributeError), and the CalculiX/SU2 downloads occasionally fail without a read timeout. Fixed all of those along the way, plus replaced the global docker compose detection with lru_cache and separated build vs solver timeouts.
Tested on macOS build, 3-participant solver run (500 timesteps), and field comparison all passed.
Reference results are generated (24MB). LFS pointer is committed but the binary needs uploading to the preCICE LFS server , happy to share the file directly if needed.