Fastsurfer Singularity workflow to quick test new code before merging

[taha-abdullah]

This PR adds a workflow to test new code inside a Singularity container, running on a local runner, before it is merged into the dev branch. It also adds some quick tests to evaluate the new code and includes documentation for how to set up and run the workflow and tests.

.github/workflows/

fastsurfer_singularity.yaml

• workflow to build and test new code in a Singularity container running on a local GitHub Actions runner

singularity_workflow.md

• dcumentation explaining how to run fastsurfer_singularity.yaml

test/

quick_test/

• test_file_existence.py

  • unittest to check if all necessary files are present in FastSurfer output

• test_errors.py

  • unittest to check if errors are present in FastSurfer log files

data/

• files.yaml

  • YAML file containing filenames that should be present in FastSurfer output

• errors.yaml

  • YAML file containing error criteria

Switching from Docker to Singularity: The workflow originally used Docker but was switched to Singularity later on.