10C Inc 3 + 4: I/O and text — the app's whole OCP surface is bound

138/138 symbols across 53 modules. New: IFSelect, Interface, XSControl,
IGESData, STEPControl, IGESControl, RWStl, Graphic3d, NCollection, StdPrs.

**The full app suite passes against this wheel: 1797 passed, 1 skipped — the
same result as the stock wheel**, run from the parity venv.

Getting there needed six methods that no static analysis could have found:
`inventory --check` only sees symbols reached through an import, so a method
called on an instance is invisible to it. The suite found them in one pass, and
one of them (gp_Vec.Reverse, which every outward-normal probe calls) accounted
for 311 of the 255 failing tests on its own. The others: gp_Trsf.SetMirror over
a plane and a point, Geom_Surface.D0, BRep_Builder.MakeFace from a
triangulation, MakePipeShell.SetMode with a fixed binormal, and MakeFace from a
surface plus tolerance.

Open question **S5 is settled: no**. The wheel does not need OCCT's share/
resources. test_inc3_io.py asserts no CSF_* variable is set and then round-trips
STEP and IGES, reading the declared units back off both — which is exactly the
resource-less container the question was about.

The XSTEP readers keep the GIL, amending the blanket "file readers and writers"
line in design.md's GIL policy. STEP and IGES traffic in process-global
Interface_Static state, the IGES reader is documented as not thread-safe, and
the app already serialises imports behind a lock — so holding it costs nothing
and removes a class of question. RWStl, which touches no global state, releases.

XSControl_Reader and IGESData are registered although the app imports neither:
they are the reader base both concrete readers inherit their transfer surface
from, and the model-to-global-section chain the IGES unit probe walks.

src/modules/mod_NCollection.cpp

@@ -0,0 +1,32 @@
+/*
+    OCP.NCollection — the UTF-8 string the font API takes.
+
+    NCollection_Utf8String is the only NCollection type the app names directly:
+    it wraps the font path and the text to emboss.  Constructed from a Python
+    str, which nanobind hands over as UTF-8 already.
+*/
+
+#include "../common/occt_module.h"
+
+#include <NCollection_String.hxx>
+
+void register_NCollection(nb::module_ &root) {
+    nb::module_ m = ocp_submodule(root, "NCollection");
+
+    nb::class_<NCollection_Utf8String>(m, "NCollection_Utf8String")
+        .def(nb::init<>())
+        // Upstream also offers an explicit-length overload; the app always
+        // passes a whole Python str, which arrives NUL-terminated, so only the
+        // one-argument form is bound.
+        .def(
+            "__init__",
+            [](NCollection_Utf8String *self, const char *text) {
+                new (self) NCollection_Utf8String(text);
+            },
+            "theCopy"_a)
+        .def("ToCString", &NCollection_Utf8String::ToCString)
+        .def("Size", &NCollection_Utf8String::Size)
+        .def("Length", &NCollection_Utf8String::Length)
+        .def("IsEmpty", &NCollection_Utf8String::IsEmpty)
+        .def("__str__", &NCollection_Utf8String::ToCString);
+}