feat: complex linetype text elements and ellipse quadrant snaps

Complex linetypes now render embedded text elements (e.g. GAS_LINE's
"GAS" labels): the LtSegment::Text variant is parsed from LIN files,
scaled along with shape/dash segments, and tessellated via
cxf::tessellate_text_ex aligned to the linetype direction.

Full ellipses gain four Quadrant snap hints at ±major/±minor axis
endpoints in addition to the existing Center snap, matching AutoCAD
snap behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/entities/mod.rs

@@ -22,7 +22,7 @@ pub mod shape;
 pub mod solid;
 pub mod spline;
 pub mod text;
-mod text_support;
+pub(crate) mod text_support;
 pub mod table;
 pub mod tolerance;
 pub mod traits;