Color arrays

[almarklein]

The gfx.Color object stores colors internally as 4 floats in a small ctypes array (ctypes.c_float * 4). One reason for doing it this way is that it could be a view on a larger array. I don't think it can be made to work just yet, but with a few changes it should be possible to have something like:

colors_array = np.zeros((100, 4), np.float32)
color = gfx.Color.from_array_and_index(colors_array, 10)

This might be convenient because this is more efficient (and convenient?) way to store colors instead of storing an array of Color objects.

To be clear: probably needs some work in pygfx to make this work. I think its probably a good idea to think about what the ideal API be like from the pov of Fastplotlib and then probably implement that in pygfx.

[kushalkolar]

I think this would be very useful for parse_colors() int graphics/_features/utils.py!

Currently in the graphic features PR:

https://github.com/fastplotlib/fastplotlib/pull/473/files#diff-ab7aaaaba02f140755a43d64627e6f9b8be46cf1f9559282e42727058ab46ee5R9-R89

This is now the only place where colors are parsed for setting line or scatter point colors.

(ignore the key argument, still have to clean it up a bit)