Own bulk-API ndarray buffers with std::vector, pin nanobind below 3

face_grid leaked both buffers when the kernel threw mid-grid, and tess copied
every mesh array a second time. Also drop the stale S5 references.

src/modules/mod_STEPControl.cpp

@@ -13,9 +13,8 @@
     The GIL stays held throughout, per the note in mod_XSControl.cpp: XSTEP is
     built on process-global state and the app serialises imports anyway.
 
-    This is also where the S5 question lands (design.md): whether the wheel has
-    to ship OCCT's share/ resources for STEP to resolve units in a container
-    with no CSF_* environment.  tests/test_inc3_io.py answers it.
+    The wheel ships none of OCCT's share/ resources; STEP still resolves units
+    in a container with no CSF_* environment, which tests/test_inc3_io.py pins.
 */
 
 #include "../common/occt_module.h"