Add measurement labels with new label_format option

[dstotz]

Adds a new label_format option that can be used to specify an option to allow for displaying measurements of a part instead of or in addition to the generators provided label. Made description the default option to preserve existing behavior.

Example of new behavior

[dstotz]

Wasn't sure what the best formatting here would be for the measurements. Do you have an opinion on if it should be a clamped float like current, rounded to the 2nd or 3rd decimal, or even potentially an integer if it's a round number?

ex alternative format int(n) if n == int(n) else round(n, 3)