Meson and distutils ways of doing things

Old workflows (numpy.distutils based):

1. python runtests.py
2. python setup.py build_ext -i + export PYTHONPATH=/home/username/path/to/numpy/reporoot (and then edit pure Python code in NumPy and run it with python some_script.py).
3. python setup.py develop - this is similar to (2), except in-place build is made permanently visible in env.
4. python setup.py bdist_wheel + pip install dist/numpy*.whl - build wheel in current env and install it.
5. pip install . - build wheel in an isolated build env against deps in pyproject.toml and install it. Note: be careful, this is usually not the correct command for development installs - typically you want to use (4) or pip install . -v --no-build-isolation.

New workflows (Meson and meson-python based):

1. spin test
2. pip install -e . --no-build-isolation (note: only for working on NumPy itself - for more details, see IDE support & editable installs)
3. the same as (2)
4. python -m build --no-isolation + pip install dist/numpy*.whl - see pypa/build.
5. pip install .