Add PyDantic/attrs-style validation to all public functions

[JoeZiminski]

It would be nice to properly validate all inputs to public functions. This could be done following the movement way.

Currently this is done ad-hoc in datashuttle e.g. #375. This should be reworked to be centralised in a argument-validation module.

[niksirbi]

See neuroinformatics-unit/movement#24 and the linked articles to make an informed decision on PyDantic vs attrs. They both do very similar things, but int he end I went with attrs for movement.

[JoeZiminski]

Thanks @niksirbi I think it makes sense to follow your lead, also good for consistency across NIU repos.