[Feature] Include a datalad centric way of downloading validation data files

[mdenker]

Feature Recently Neo moved towards github actions to carry out those unit tests taking in gin data using datalad. This is an approach to consider in our efforts to increase validation testing:

• Run unit tests based on datasets only for certain commits (e.g., PRs)
• Efficient download and caching of the datasets.

For details, see github actions defines in python-neo.