Add shared spline_ops module with:
- spline_to_bspline / bspline_to_spline: acadrust ↔ truck BSplineCurve conversion
- spline_sample_xy: sample DXF-XY projection at N+1 points with parameters
- spline_nearest_t: nearest-parameter search via coarse+bisection
- spline_pts_wire: world-space wire points for WireModel preview
TRIM: Spline entities can now be used as cutting boundaries (Geo::Spline
sampled into polyline segments) and as entities being trimmed; uses
BSplineCurve::cut() to produce surviving pieces.
EXTEND: extend_spline() shoots a tangent ray from the nearest endpoint
and appends a control point at the first boundary hit.
OFFSET: offset_spline() offsets each sample point along the local
perpendicular normal and rebuilds a new spline from the offset control pts.
BREAK: break_spline() uses spline_nearest_t() + BSplineCurve::cut() to
split the spline at one or two click points.
LENGTHEN: lengthen_spline() uses numerical arc-length integration +
bisection to cut the spline at the parameter corresponding to the new
requested length.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
