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

README.md

@@ -51,6 +51,22 @@ import n3xd_ocp
 areas, centroids = n3xd_ocp.measure.face_surface_props(result)   # one call for every face
 meshes = n3xd_ocp.tess.extract_meshes(result)                    # triangulated faces, ready to render
 data = n3xd_ocp.bintools.write_bytes(result)                     # BREP bytes, no temp file needed
+
+points, normals, uv_bounds = n3xd_ocp.sample.face_grid(face, 33)  # a 33x33 UV grid on one face
+```
+
+`n3xd_ocp.helix` reaches OCCT 8.0's TKHelix, which upstream has no binding for. For N segments it wants N pitches, N turn counts and **N+1 diameters** — one per segment boundary, so consecutive values that differ taper across that segment:
+
+```python
+from OCP.gp import gp_Ax3, gp_Dir, gp_Pnt
+
+axis = gp_Ax3(gp_Pnt(0, 0, 0), gp_Dir(0, 0, 1), gp_Dir(1, 0, 0))
+wire, tolerance_reached = n3xd_ocp.helix.pure_helix(axis, 8.0, [1.25], [12.0])
+
+builder = n3xd_ocp.helix.BuilderHelix()                  # tapered, e.g. an NPT thread
+builder.set_parameters(axis, [10.0, 8.0], [2.0], [4.0])
+builder.set_approx_parameters(1.0e-4)
+builder.perform()
 ```
 
 ## Build