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]

@makis, would love your feedback while adding the test suite I ran into a few things locally Ubuntu 24.04 has a default user with UID/GID 1000 which breaks the container build, some adapter ARGs were missing defaults which caused issues when building standalone, and the CalculiX and SU2 downloads occasionally fail without retries. Fixed all of those along the way. Let me know if anything needs changing!