tools/bench_ext.py: measure the bulk APIs against the loops they replace

Keeps the numbers next to the code rather than in a commit message, since the
adoption decisions turn on them. Two results are not what the plan assumed:

- face_surface_props gains *nothing* from leaving Python — the serial C++ loop
  costs exactly what the Python loop costs. That agrees with the app's own
  profile, which found SurfaceProperties to be 94 % of face_candidate_anchors:
  the time is inside the kernel, so the interpreter round trip was never the
  problem. The whole 10.9x is OSD_Parallel, reachable only because the GIL is
  released.
- BinTools is already fast enough. Dropping the BytesIO detour saves nothing
  measurable, so the pools' overhead is not in serialisation — worth knowing
  before rewriting seventeen call sites for it.

Mesh extraction is the clear win at 35x, where the Python loop overhead really
does dominate; edge polylines 2.6x.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DfriM8XUkn7uYf5Dwe2xo6

pyproject.toml

@@ -9,7 +9,7 @@ name = "n3xd-ocp"
 # .devN suffix: the registry never allows republishing a version, and its
 # cleanup rule collects only the dev ones.  CMake asserts the prefix matches
 # the OCCT it found.
-version = "7.9.3.1.dev4"
+version = "7.9.3.1.dev5"
 description = "nanobind bindings for the OpenCASCADE geometry kernel (drop-in OCP)"
 readme = "README.md"
 requires-python = ">=3.12"