Show resolved unit symbols in read-only Pset/Qto view; add write-back and fallback regression tests

Previously, unit symbols only appeared while a Pset/Qto was in edit mode
(pencil icon) -- the read-only summary view read raw {name: value} dicts
straight from ifcopenshell.util.element.get_psets(), a completely separate
path from the Attribute/unit_symbol machinery, so it never showed a label
even after the earlier fixes. This matters for the "someone in the field
just looking at values" use case, not just editing.

- bim/module/pset/data.py: switch to get_psets(verbose=True) to get each
  property's own entity id, then resolve its unit symbol the same
  override-aware way the edit-mode path does (tool.Pset.get_unit_symbol_for_prop).
  Falls back gracefully (empty symbol) for IfcPreDefinedPropertySet
  attributes, which aren't IfcProperty entities and can't carry a Unit
  override.
- bim/module/pset/ui.py: read-only value button now shows "250 mm" instead
  of just "250".

Also adds the regression tests planned but not yet committed:
- test/tool/test_pset.py: edit a property with its own Unit override and
  write it back, confirming no rescale and the override survives.
- test/bim/test_prop.py (new): get_display_name() falls back to the plain
  name (no crash) when no unit is resolvable or the project has no units
  assigned at all.

src/bonsai/test/bim/test_prop.py

@@ -0,0 +1,79 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2026
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+
+import bpy
+import ifcopenshell
+import ifcopenshell.api.pset
+import ifcopenshell.api.root
+import ifcopenshell.api.unit
+
+import bonsai.tool as tool
+from test.bim.bootstrap import NewFile
+
+
+def import_single_property(ifc, element, prop):
+    """Import a single existing IfcProperty into a real, addon-registered
+    PsetProperties collection, exactly as the property editor does, and
+    return its `metadata` (an `Attribute`)."""
+    pset = ifcopenshell.api.pset.add_pset(ifc, product=element, name="Pset_Test")
+    pset.HasProperties = [prop]
+    obj = bpy.data.objects.new(prop.Name, None)
+    tool.Ifc.link(element, obj)
+    props = obj.PsetProperties
+    tool.Pset.import_pset_from_existing(pset, props, None)
+    return props.properties[prop.Name].metadata
+
+
+class TestGetDisplayName(NewFile):
+    def test_appends_the_resolved_unit_symbol(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        pressure = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="PRESSUREUNIT")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[pressure])
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcPressureMeasure(5.0))
+        metadata = import_single_property(ifc, element, prop)
+
+        assert metadata.display_name == "Foo, Pa"
+
+    def test_falls_back_to_the_plain_name_when_no_unit_is_resolvable(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        # No units assigned to the project at all -- nothing to resolve.
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcPressureMeasure(5.0))
+        metadata = import_single_property(ifc, element, prop)
+
+        assert metadata.unit_symbol == ""
+        assert metadata.display_name == "Foo"
+
+    def test_falls_back_to_the_plain_name_for_a_non_measure_property(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcText("Bar"))
+        metadata = import_single_property(ifc, element, prop)
+
+        assert metadata.unit_symbol == ""
+        assert metadata.display_name == "Foo"