Some libraries with general support for logarithmic units:

Astropy.units (Python): https://docs.astropy.org/en/stable/units/logarithmic_units.html

PhysicalQuantities (Python): https://pypi.org/project/PhysicalQuantities/ - one of the four main goals: "provide logarithmic dB calculations"

Pint (Python): https://pint.readthedocs.io/en/stable/user/log_units.html

JScience (Java): https://javadoc.io/static/org.jscience/jscience/4.3.1/javax/measure/unit/NonSI.html#DECIBEL

UDUNITS (C): https://docs.unidata.ucar.edu/udunits/current/ - logarithmic units "are fully integrated into the package and all meaningful operations and conversions are supported"