Temporal scales don't work in scatterplots

[jameshadfield]

Current Behavior

Colourings with a temporal scale (except for num_date) do not work in scatterplots, with NaNs appearing in the SVG coordinates, e.g.:

Error: <path> attribute d: Expected number, "MNaN 472.09999999…".

They should behave similarly to how num_date currently does, however all nodes without metadata values (usually all internal nodes and perhaps some tips) should not appear. Scatterplots already have the ability to hide nodes which don't have appropriate metadata (e.g.).

This was first identified in #1832 but it predates that PR.

How to reproduce

1. Create a dataset with a temporal scale (values can be numerical or, if you're using a version of Auspice more recent than c585722 they can be YYYY-MM-DD)

2. View a scatterplot with the temporal scale as the x or y axis.

[jameshadfield]

Whoops, this behaviour is unique to the YYYY-MM-DD temporal values introduced in #1832, my mistake. If the values themselves are numeric then we get the appropriate behaviour, e.g. this for rabies divergence vs sampling year: