I've seen a few before, and a quick search yielded a bunch for me, right off the bat. By no means exhaustive:

Julia: https://github.com/PainterQubits/Unitful.jl

Python: https://pint.readthedocs.io/en/0.6/

C++: https://github.com/nholthaus/units

etc.

And yes, it has always struck me as strange that date/time/calendar utilities are standard as canonical functionality shipped with language distributions, but units are not.