`Attrib` gains optional per-attribute properties (`props`), each overriding
the attribute definition's. DXF reading takes them from the ATTRIB's groups
8/6/62/420/370; writing gives each ATTRIB the properties it is drawn with.
The renderer prefers them over the definition's. -ATTEDIT's Layer and Color
options set them; ATTSYNC resets them to the definitions, as in AutoCAD.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
