NDData show units

[nstarman]

Description

Now NDData with units shows the units on str() and repr(). Importantly, repr maintains its current level of fidelity to eval(repr(x)) == x (I add a check for this to the tests)

>>> x = NDData([1, 2, 3], unit="km")
>>> print(repr(x))
NDData([1, 2, 3], unit='km')

>>> print(str(x))
[1 2 3] km

@mhvk @saimn @mwcraig

Fixes #11541

Followup ideas:

• eval(repr(x)) == x doesn't actually work for NDData, with or without units, even if they are identical attribute-by-attribute. Modding __eq__ would be good.
• show other attributes in string representations: mask, uncertainty, ...

[saimn]

👍 for me, but @mwcraig should approve as the nddata maintainer.

[mwcraig]

thanks, @nstarman, this looks great!

[mwcraig]

eval(repr(x)) == x doesn't actually work for NDData, with or without units, even if they are identical attribute-by-attribute. Modding __eq__ would be good.

I opened an issue for this at #11648