Phase 10A/10B Inc 0: build system, handle model, first module surface

Builds n3xd-ocp end to end and publishes 7.9.3.1.dev1 to the Gitea registry,
where it installs anonymously and passes its suite.

- occt/Dockerfile: OCCT 7.9.3 compiled once into a manylinux_2_28 builder
  image (base digest + tarball sha256 pinned), Draw/VTK/Tk/Xlib/OpenGL off,
  FreeType on, -O2 without fast-math or march=native. A final layer asserts
  TKService/TKV3d exist with no libGL/libX11 DT_NEEDED, which is what lets the
  app image drop libgl1/libx11-6. Mounted into, never built FROM.
- scikit-build-core + nanobind STABLE_ABI -> one cp312-abi3 extension that
  registers every OCP.* submodule via PyImport_AddModule, so `import
  OCP.TopoDS` needs no shim and cls.__module__ is right. Version <occt>.N is
  asserted against the OCCT found, keeping occt_version() truthful.
- occt_handle.h: type caster for opencascade::handle<T> over OCCT's intrusive
  refcount. Wrappers are non-owning instances holding exactly one handle in
  their keep-alive list, reusing an existing wrapper so identity survives a
  round trip. Transient constructors go through ocp_new (never nb::init<>,
  which would let OCCT delete nanobind's storage); the caster refuses a
  refcount-0 object rather than corrupt the heap. Verified under ASAN with no
  memory-safety errors, plus an RSS bound over 50k create/destroy cycles.
- Sub-shapes are returned by value everywhere, making the TShape lifetime class
  that segfaulted a process-global face memo unrepresentable.
- Standard_Failure derives RuntimeError, with ~20 concrete types dispatched on
  the dynamic OCCT type (cad_pool marshals failures home by type name).
- Inc 0 surface: gp subset, TopAbs, TopoDS (+ downcasts), TopExp, TopLoc,
  TopTools, BRep, BinTools, Poly, Standard. 34 of the app's 139 symbols.
- n3xd_ocp: additive APIs kept out of the OCP namespace so parity testing stays
  meaningful. bintools (shape <-> bytes, GIL-free, byte-identical) and _debug.

Two findings worth the record, both verified against the stock wheel rather
than assumed: upstream binds __hash__ but leaves __eq__ at identity, which is
exactly what geom_memo.py's hash-bucket + IsSame scan is built around, so we
match it instead of "fixing" it; and BinTools can release the GIL after all, by
slurping the file-like object instead of bridging a streambuf that would call
back into Python.

Gate: BREP round-trips are byte-identical to cadquery-ocp-novtk across six
fixtures (the generator asserts stock idempotency first). That matters beyond
IPC — derive.py content-addresses BREP payloads by sha256 and stores the ref.

tests/data/manifest.json

@@ -0,0 +1,36 @@
+{
+  "generated_by": "cadquery-ocp-novtk",
+  "occt_version": "7.9.3.1",
+  "shapes": {
+    "box": {
+      "sha256": "d83ce546f116c93596552ed7628736843c05a6455c13d9e209a0c2830bd6cc35",
+      "size": 4494,
+      "faces": 6
+    },
+    "box_meshed": {
+      "sha256": "b656381c0fd05aae37256e36e15d038a80c5f10df0a4ef4ee570192d23772896",
+      "size": 6931,
+      "faces": 6
+    },
+    "fused": {
+      "sha256": "3535742144c0a789f06b6a1950c5cecfc723e9bfeaf3b3b5cb7c38c78027661e",
+      "size": 10602,
+      "faces": 12
+    },
+    "cut_cylinder": {
+      "sha256": "f91914a18d5faa9ffbb213f46257f00d3a08c09d58f7de96820d7f7431391e8f",
+      "size": 6058,
+      "faces": 7
+    },
+    "located_compound": {
+      "sha256": "4214e4a24a419d0ee7cdc1db113740a645d37ff696a18924bbed602535a8896f",
+      "size": 4618,
+      "faces": 12
+    },
+    "empty_compound": {
+      "sha256": "396c108ce1871b60b5076fddd4baa0266797a2294b4a401a689a9ed7ca1e2de0",
+      "size": 171,
+      "faces": 0
+    }
+  }
+}