Should we merge IfcTimeMeasure and IfcDuration?

> If you wanted to push this farther one could also fix units for the value "Warranty Duration" to be months as warranties on typical building products range from 12 to 60 months.

In the core spec we don't have nominated units for properties, only measures.

In this case WarrantyPeriod is IfcDuration http://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcDuration.htm

> EXAMPLE: P2Y10M15DT10H30M20S (duration of two years, 10 months, 15 days, 10 hours, 30 minutes and 20 seconds).

It seems much more logical to me to have a IfcConversionBasedUnit for months, the examples there already list days:

> 'day' Time measure equal to 86400 s

Do we need both IfcTimeMeasure and IfcDuration? Can we have a discussion on the merits of each and which to apply where?

Advantages of the numeric IfcTimeMeasure:
- more efficient
- support arithmetic
- arbitrary precision because floating point
- ...

_Originally posted by @aothms in https://github.com/buildingSMART/IFC4.3.x-development/issues/54#issuecomment-1046186166_