sql, stream: raise for accessing derived attributes

Raising `AttributeError` is definitely wasn't correct here, since it
might push the code to assume it's a wrong entity type. Returning some stub value like `None` also could suggest incorrect derived attribute
value, leading to unexpected behaviour. So adding an error, so it would
propagate and code would need to be adjusted not to rely on derived
attributes, if it actually interacts with sql/stream.

`test_unit` was asserting that derived attr will return `None`, though
it was actually raising `AttributeError`.

src/ifcopenshell-python/test/test_sql.py

@@ -19,6 +19,7 @@
 import tempfile
 from pathlib import Path
 
+import pytest
 from ifcpatch.recipes import Ifc2Sql
 
 import ifcopenshell
@@ -63,6 +64,12 @@ class TestEntity:
         assert (element := ifc_sqlite.by_id(1))
         assert element.Name == "My Project"
 
+    def test_getattr_derive(self):
+        ifc_sqlite = get_ifc_sqlite()
+        assert (units := ifc_sqlite.by_type("IfcSIUnit"))
+        with pytest.raises(RuntimeError):
+            units[0].Dimensions
+
     def test_setattr(self):
         ifc_sqlite = get_ifc_sqlite()
         assert (element := ifc_sqlite.by_id(1))