feat: units integration

[seanpearsonuk]

• Support units for settings API parameters.
• Controlled by the "units-quantity" attribute since "quantity-map" is not yet there.
• Quantity to name mappings are held in a Python dictionary that is generated via lispy.parse(...).
• Special attention is given to the possibility of a leading "'" in names. That will be a reality in the console, but not in PyFluent.