circle ci testing vs local integration tests

[stnava]

circleci has limited available memory with the free plan -- as such we must keep the continuous integration testing to a bare minimum as evidenced here: https://github.com/ANTsX/ANTsPyMM/blob/main/.circleci/config.yml

pytest identifies anything under ANTsPyMM/*/*test*py as a test

currently this is only

(myenv-311) mac:ANTsPyMM stnava$ ls */*test*py
tests/test_loop.py		tests/test_nrg_validation.py	tests/test_reference_run.py

the docs folder -- on the other hand -- contains several examples of possible ANTsPyMM usage that, in some cases, depend on data that the user may not have e.g. UK Biobank data.

we therefore differentiate three types of example scripts:

1. tests on circleci as ANTsPyMM/*/*test*py -- these will just test that the package can be loaded and basic operations can be performed.
2. tests that can be run locally (or in a container) as ANTsPyMM/*/*localint*py -- these will take longer to run and will be both high level ( eg of the mm function ) or modality specific. these should be run regularly but not necessarily on all commits.
3. other examples will be the other files in docs/ that are not in one of the two cases above ( e.g. how to compute perfusion from data available in the NNL ). these are for illustrations and not regularly tested and, as such, are likely to fall out of date over time.