Extended FilletCommand and ChamferCommand to accept Lines and Arcs as
first/second entity. Added fillet_line_arc() and fillet_arc_arc()
geometry functions that find a tangent fillet circle between the two
entities, trim each to the tangent point, and insert the fillet arc.
r=0 case trims/extends to the nearest intersection without inserting an arc.
Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
