* Added AreaNthSelector
Added AreaNthSelector that is useful for nested features selection. Especially to select one of coplanar nested wires for subsequent extrusion, cutting or filleting.
* LengthNthSelector
* Explicitly marked _NthSelector class and _NthSelector.key(..) method as abstract using standard abc package
* AreaNthSelector ignores "bad" Wires
AreaNthSelector.key raises ValueError if temporary face creation fails for a wire for any reason (non-planar, non-closed). That causes _NthSelector that it inherits to ignore such wires. Done so for consistency with RadiusNthSelector that ignores anything it can not get radius from.
Co-authored-by: Marcus Boyd <mwb@geosol.com.au>
