Add bulk UV sampler, TKHelix and MakeSphere (8.0.1.2)

- n3xd_ocp.sample.face_grid: a face's UV grid of points and outward
  normals in one GIL-free call, sampling exactly where np.linspace does
  so a caller's fitted surface does not move.
- n3xd_ocp.helix: OCCT 8.0's TKHelix, which upstream does not bind at
  all. Takes Python lists rather than NCollection_Array1. Two things the
  header does not say, both found by probing: SetParameters wants N+1
  diameters for N segments (one per boundary, so a taper interpolates),
  and the builder is right-hand only -- a negative pitch is error status
  12, not a mirrored helix.
- Bind BRepPrimAPI_MakeSphere and give inventory.py an EXTRA_SYMBOLS
  addendum for symbols no app source imports. assay's gen_flow_fixtures
  has been unrunnable since the 10C cutover for want of it; the gap was
  wider than --check, since sigdiff is inventory-driven too.

Gates: 105 tests, 139/139 symbols, sigdiff clean, ASAN clean, wheel
self-contained with no libGL/libX11 DT_NEEDED.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HbTQ2HYWQwdtGmGJwypt6Z

tests/test_ext_helix.py

@@ -0,0 +1,118 @@
+"""n3xd_ocp.helix — OCCT 8.0's TKHelix builder.
+
+The toolkit is new in 8.0 and has no upstream binding to compare against, so
+these are property checks rather than a parity gate: the wire has to be a real
+helix of the requested pitch and turn count, and the failure modes have to
+surface as Python exceptions rather than a silently empty shape.
+"""
+
+from __future__ import annotations
+
+import math
+
+import pytest
+
+import n3xd_ocp
+from OCP.BRepGProp import BRepGProp
+from OCP.GeomAbs import GeomAbs_C1, GeomAbs_C2
+from OCP.gp import gp_Ax3, gp_Dir, gp_Pnt
+from OCP.GProp import GProp_GProps
+from OCP.TopAbs import TopAbs_EDGE
+from OCP.TopExp import TopExp
+from OCP.TopTools import TopTools_IndexedMapOfShape
+
+AXIS = gp_Ax3(gp_Pnt(0, 0, 0), gp_Dir(0, 0, 1), gp_Dir(1, 0, 0))
+
+
+def _length(shape) -> float:
+    props = GProp_GProps()
+    BRepGProp.LinearProperties_s(shape, props)
+    return props.Mass()
+
+
+def _edge_count(shape) -> int:
+    edges = TopTools_IndexedMapOfShape()
+    TopExp.MapShapes_s(shape, TopAbs_EDGE, edges)
+    return edges.Extent()
+
+
+def test_single_segment_has_the_right_arc_length():
+    """One turn of a helix is sqrt(circumference^2 + pitch^2) long."""
+    diameter, pitch, turns = 8.0, 1.25, 1.0
+    wire, reached = n3xd_ocp.helix.pure_helix(AXIS, diameter, [pitch], [turns])
+    expected = turns * math.hypot(math.pi * diameter, pitch)
+    assert _length(wire) == pytest.approx(expected, rel=1e-4)
+    assert reached > 0.0
+    assert _edge_count(wire) >= 1
+
+
+@pytest.mark.parametrize("turns", [0.5, 3.0, 24.0])
+def test_arc_length_scales_with_the_turn_count(turns):
+    diameter, pitch = 8.0, 1.25
+    wire, _reached = n3xd_ocp.helix.pure_helix(AXIS, diameter, [pitch], [turns])
+    expected = turns * math.hypot(math.pi * diameter, pitch)
+    assert _length(wire) == pytest.approx(expected, rel=1e-4)
+
+
+def test_variable_pitch_segments_compose():
+    """The array form is the reason this is bound at all — a spring whose
+    pitch changes partway is one wire, not two."""
+    diameter = 10.0
+    wire, _reached = n3xd_ocp.helix.pure_helix(
+        AXIS, diameter, [2.0, 5.0], [3.0, 2.0]
+    )
+    expected = 3.0 * math.hypot(math.pi * diameter, 2.0) + 2.0 * math.hypot(
+        math.pi * diameter, 5.0
+    )
+    assert _length(wire) == pytest.approx(expected, rel=1e-3)
+
+
+def test_tapered_diameters_via_the_builder():
+    """Two segments, so three boundary diameters: 10 -> 8 tapering, then 8 -> 8
+    straight.  A tapered thread (NPT) is the reason the array form is bound."""
+    builder = n3xd_ocp.helix.BuilderHelix()
+    builder.set_parameters(AXIS, [10.0, 8.0, 8.0], [2.0, 2.0], [2.0, 2.0])
+    builder.set_approx_parameters(1.0e-4, 8, GeomAbs_C1)
+    builder.perform()
+    assert builder.error_status() == 0
+    # The straight half is exact; the tapered half is longer than a cylinder of
+    # its smaller diameter and shorter than one of its larger.
+    straight = 2.0 * math.hypot(math.pi * 8.0, 2.0)
+    largest = 2.0 * math.hypot(math.pi * 10.0, 2.0)
+    total = _length(builder.shape())
+    assert straight * 2 < total < straight + largest
+
+
+def test_the_n_plus_one_diameter_rule_is_enforced():
+    """OCCT wants N+1 diameters for N segments and raises
+    Standard_ConstructionError otherwise; the binding checks it first so the
+    message names the shape it wanted."""
+    builder = n3xd_ocp.helix.BuilderHelix()
+    with pytest.raises(ValueError, match="N\\+1 diameters"):
+        builder.set_parameters(AXIS, [8.0], [1.25], [1.0])
+    builder.set_parameters(AXIS, [8.0, 8.0], [1.25], [1.0])  # accepted
+
+
+def test_continuity_is_selectable():
+    wire_c1, _ = n3xd_ocp.helix.pure_helix(
+        AXIS, 8.0, [1.25], [2.0], continuity=GeomAbs_C1
+    )
+    wire_c2, _ = n3xd_ocp.helix.pure_helix(
+        AXIS, 8.0, [1.25], [2.0], continuity=GeomAbs_C2
+    )
+    assert _length(wire_c1) == pytest.approx(_length(wire_c2), rel=1e-3)
+
+
+def test_mismatched_segment_arrays_are_rejected():
+    with pytest.raises(ValueError):
+        n3xd_ocp.helix.pure_helix(AXIS, 8.0, [1.0, 2.0], [1.0])
+    with pytest.raises(ValueError):
+        n3xd_ocp.helix.pure_helix(AXIS, 8.0, [], [])
+
+
+def test_builder_rejects_ragged_parameters():
+    builder = n3xd_ocp.helix.BuilderHelix()
+    with pytest.raises(ValueError):
+        builder.set_parameters(AXIS, [8.0, 8.0], [1.0], [1.0, 2.0])
+    with pytest.raises(ValueError):
+        builder.set_parameters(AXIS, [8.0, 8.0], [], [])