STEP export: unique ids, plain curves, right revolution senses; seams on split faces

Vendored truck-stepio (writer only): an intersection curve's second surface
was written at the first one's id (duplicate ids for every boolean edge),
and revolved surfaces lost their orientation (the modeling-surface sense was
always true; inverted or mirrored revolutions came out inside out). Export
now writes intersection edges as C1 cubic B-splines through exact points,
so files carry plain 3D curves and no redundant surfaces.

Vendored truck-meshalgo: hinted parameter searches that run off a B-spline's
domain are rejected or clamped (meshing their grid never finished).

STEP import: straight revolution profiles are bounded in the meridian plane
and stop at the axis; loops on revolutions start away from the axis; face
extents include edge end points. Edges between pieces of one split surface
draw as seams.

kernel::step_validate checks a STEP file (duplicate ids, dangling
references, dense numbering); the oracle replay now exports every rebuilt
part, validates it and re-imports it with no warnings and the same volume
(all 32 rebuildable cases pass).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

Cargo.lock

@@ -3525,8 +3525,6 @@ dependencies = [
 [[package]]
 name = "truck-meshalgo"
 version = "0.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e18f325738e822c79bb1a48897ec789cbf50cbeeb0841105295f9da85bdf3613"
 dependencies = [
  "array-macro",
  "derive_more",
@@ -3591,8 +3589,6 @@ dependencies = [
 [[package]]
 name = "truck-stepio"
 version = "0.3.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2d29cf5b0dec4b927e80b5dca26ce3ca69601c77ea5b9c953e30bfc3e123d189"
 dependencies = [
  "chrono",
  "truck-geometry",