Gate slab disconnect gizmos behind parametric edit lifecycle

Wires slabs into the parametric edit framework (tool.Parametric
.EDIT_TYPES) so the wall-slab disconnect UI gets ESC handling, red
cancel icon, mutual exclusion with other parametric edits, and
per-feature gizmo prefs — all from BaseParametricGizmoGroup — without
duplicating the lifecycle.

Adds:
- ParametricObject("slab") registry entry + tool.Parametric.is_slab
  predicate (any IfcSlab).
- BIMSlabProperties with is_editing flag; PointerProperty wired by
  the framework's register_object_properties.
- bim.enable_editing_slab / bim.finish_editing_slab /
  bim.cancel_editing_slab operators on tool.Ifc.Operator so they
  flow through tool.Parametric.run_bim_op cleanly. No IFC mutation
  — slab edit is a pure UI gate; finish and cancel share the body.
- tool.Model.get_slab_props accessor.
- GizmoSlabEdition inheriting BaseParametricGizmoGroup with the
  pen / validate / cancel triad. is_element_type narrows to
  IfcSlab with at least one wall clipped to its underside.

The disconnect-icon group GizmoSlabUnjoinWalls polls behind
_slab_connection_gizmo_poll_gate(require_editing=True), which now
reads is_editing through tool.Model.get_slab_props.

Drops the standalone GizmoSlabConnectionAccess + the
setup_pen_cancel_icons helper added earlier in this branch — both
superseded by the framework integration.

Also folds in the wall + multi-slab gizmo polish requested live:
- Wall side: stack the per-slab unjoin icons vertically (up to 5)
  so multi-slab connections each get a distinct clickable icon;
  hover-highlight reveals which slab will disconnect.
- GizmoPairDisconnect activates when 2 elements with an
  IfcRelConnectsElements(TOP) rel are selected, with the icon at
  the wall-slab connection world anchor.
- Wall-slab anchor moved from slab clip Z to wall top +
  WALL_SLAB_CONNECTION_Z_CLEARANCE so the disconnect icon perches
  above the extend-vertical / slope gizmo instead of overlapping.
- Shared _resolve_active_partner_pair helper for 2-selection
  gizmos; _slab_connection_gizmo_poll_gate added to
  _REQUIRED_CALLEES + GizmoSlabEdition added to the AST
  forward-compat allowlist.

Build note: wall.py's DisconnectElements._perform imports
bonsai.core.connection.disconnect_rel — that core module is being
added in a parallel-session commit. Until that lands the addon
import will fail.

Generated with the assistance of an AI coding tool.

src/bonsai/test/bim/module/model/test_wall_array_child_filter_forward_compat.py

@@ -26,6 +26,8 @@ Allow-list (gizmos intentionally outside the rule):
 
 - ``GizmoWallEdition`` — single-object parametric edit gizmo. Its base
   parametric poll already filters array children.
+- ``GizmoSlabEdition`` — same as ``GizmoWallEdition`` (inherits
+  ``BaseParametricGizmoGroup`` whose poll filters array children).
 - ``GizmoWallFilletPreview`` — the preview-owner whose poll must fire
   WHILE its own preview is active; routing it through the topology gate
   would self-block it.
@@ -47,9 +49,11 @@ pytestmark = pytest.mark.model
 
 # Wall gizmo groups intentionally outside the rule. Add a new entry only
 # with the in-code reasoning above.
-_ALLOWLIST = frozenset({"GizmoWallEdition", "GizmoWallFilletPreview"})
+_ALLOWLIST = frozenset({"GizmoSlabEdition", "GizmoWallEdition", "GizmoWallFilletPreview"})
 
-_REQUIRED_CALLEES = frozenset({"_wall_topology_gizmo_poll_gate", "any_selected_is_array_child"})
+_REQUIRED_CALLEES = frozenset(
+    {"_wall_topology_gizmo_poll_gate", "_slab_connection_gizmo_poll_gate", "any_selected_is_array_child"}
+)
 
 
 def _wall_module_source():

src/bonsai/test/bim/module/model/test_wall_slab_connections.py

@@ -178,28 +178,30 @@ def test_find_wall_slab_rel_returns_none_when_unconnected():
 # ---------------------------------------------------------------------------
 
 
-def test_wall_slab_connection_location_lifts_axis_mid_to_slab_underside():
-    """The icon sits at the wall's axis midpoint X/Y lifted to the slab's
-    underside Z so it reads as a marker on the slab cut line."""
+def test_wall_slab_connection_location_perches_above_wall_top():
+    """Icon X/Y comes from the wall axis midpoint; Z from the wall's mesh
+    bbox top in world space plus WALL_SLAB_CONNECTION_Z_CLEARANCE so the
+    icon sits above the extend-vertical / slope gizmo at the wall top."""
     wall_obj = Mock()
-    slab_obj = Mock()
-    slab_obj.matrix_world = Matrix.Translation(Vector((0.0, 0.0, 3.0)))
-    slab_obj.bound_box = [
-        (-1.0, -1.0, 0.0),
-        (1.0, -1.0, 0.0),
-        (-1.0, 1.0, 0.0),
-        (1.0, 1.0, 0.0),
-        (-1.0, -1.0, 0.2),
-        (1.0, -1.0, 0.2),
-        (-1.0, 1.0, 0.2),
-        (1.0, 1.0, 0.2),
+    wall_obj.matrix_world = Matrix.Identity(4)
+    wall_obj.bound_box = [
+        (-0.1, -0.1, 0.0),
+        (0.1, -0.1, 0.0),
+        (-0.1, 0.1, 0.0),
+        (0.1, 0.1, 0.0),
+        (-0.1, -0.1, 3.0),
+        (0.1, -0.1, 3.0),
+        (-0.1, 0.1, 3.0),
+        (0.1, 0.1, 3.0),
     ]
+    slab_obj = Mock()
 
     ref_line = (Vector((1.0, 0.0, 0.0)), Vector((3.0, 0.0, 0.0)))
     with patch.object(tool.Wall, "get_world_reference_line", return_value=ref_line):
         loc = tool.Wall.wall_slab_connection_location_world(wall_obj, slab_obj)
 
-    assert loc == Vector((2.0, 0.0, 3.0))
+    expected_z = 3.0 + tool.Wall.WALL_SLAB_CONNECTION_Z_CLEARANCE
+    assert loc == Vector((2.0, 0.0, expected_z))
 
 
 def test_wall_slab_connection_location_returns_none_for_axisless_wall():