feat: tests

[WillForan]

• single-shot.sh runs a server just long enough for a single shot client to run
• tests/helpers has functions to
  • generates a 4x4x4 checker board and
  • read data matrix from mrd h5 files
• tests/test_invert.py inverts that using single-shot.sh
• Makefile has test and format runner not running black nor isort on existing files
• pyproject.toml is useful for pip install -e .[dev]

[WillForan]

Sorry for the unsolicited and somewhat large pull request. I'm preparing to work on custom preprocess modules and wanted to have guard rail tests (to protect against my own bad edits, but also those of the LLM). Thought they might be useful to others too.

The marquee addition might be single-shot.sh. It provides a kludgy but unattended way to exercise the code for a given module.