Handle shaped and zero-length input data in cxctime2plotdate

[taldcroft]

Description

cxctime2plotdate previously only accepted 1-d data, and crashed for a zero-length input. This fixes that.

A driver for this change was the arc/make_timeline.py was getting exceptions due to the zero-length problem.

Testing

• Passes unit tests on MacOS (with new tests)
• [n/a] Functional testing

[jeanconn]

Do we want to just update it to deal with NxM shapes or should arbitrary lists of lists just work too?

[taldcroft]

I don't see any need for arbitrary ragged lists of lists. It does currently handle an arbitrary regular list of lists (an N-dimensional cube of data) but not a ragged list of lists.

[jeanconn]

Sounds good. I was wondering if the implementation might actually be simpler but also couldn't think of a use case.

[taldcroft]

Dealing with ragged lists of lists is actually a huge pain. Unless there is a very strong driver the right answer is to delegate to np.asarray and fail if that doesn't work.