Built-in support for units

[gonzalocasas]

          I always felt we needed to add built-in/native support for units across the board. Something like what `astropy` does: https://docs.astropy.org/en/stable/units/index.html

Because, well, it's important :)

Originally posted by @gonzalocasas in https://github.com/compas-dev/compas/issues/1140#issuecomment-1533357457