clean up integration tests

[VeraChristina]

What maintenance does this project need?

Just to record a couple of small clean ups for integration tests as they kept evolving:

• simplify GetTmpPaths as we don't need shared basedir anymore (former hardware.paths.data)
• add ids for parametrized tests for readability of log
• move dataloader.X.start/end to testing_modifications since we use the same datasets for all tests
• split into different files?
• reuse fixtures/functions to reduce duplication between architecture_config, gnn_config, base_global_config (which are all global models)

CI related

• use organisation secret instead of HPC_CI_INTEGRATION_USER in integration test hpc workflow for consistency
• potentially add option to skip benchmark tests when running hpc workflow manually
• consider splitting into multiple slurm jobs. As we keep adding tests, run time and memory requirements increase

For context

Ticket for expanding the integration tests: #484