Convert Quantity to most fitting Prefix

[keilw]

I will transfer this to Indriya to explore possible functions like that.

Originally posted by @keilw in unitsofmeasurement/unit-api#236 (comment)

[puigru]

For reference, I found a units library for Python which offers something like this.

Source: https://pint.readthedocs.io/en/stable/developers_reference.html#pint.Quantity.to_compact

It also has to_base_units() which can be used to reverse the process.