Compare entity instances in one file by identity again

entity_instance.file is a property backed by a fresh SWIG wrapper on every
access, and ifcopenshell::file had no __eq__, so `self.file != other.file`
in entity_instance.__eq__ compared two throwaway wrappers and was always
true - even for an instance against itself. Every entity comparison
therefore took the deep get_info() branch, making distinct but structurally
identical instances compare equal and leaving the final `return False`
unreachable. Bonsai's TestAddRepresentationItemToShapeAspect showed this as
two separate IfcShapeAspects being treated as one, so the stale aspect was
never removed.

Restore the file_pointer() pair that was commented out on both
ifcopenshell::file and express::Base - IfcParseWrapper.i already described
it as the way to "trace file ownership of instances on the python side" -
and give file the __eq__/__hash__ it was missing. The express::Base one
needs $self->file() now that file_ lives on instance_data. This also
repairs rocksdb_lazy_instance.__eq__, which already called file_pointer().

EXPRESS `=` is value comparison and `:=:` is instance comparison, but
rule_compiler emits `==` for both (see the @todo on process_rel_op), and
derived attributes build their operands in the shared global file, so rules
compare same-file instances and need value semantics. Restore those for the
duration of rule execution with settings.compare_instances_by_value,
alongside the existing unpack_non_aggregate_inverses.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ifcopenshell-python/test/test_entity_instance.py

@@ -75,6 +75,20 @@ def test_equality():
     assert f[1] == g[1]
     g[1].Coordinates = (1.0, 0.0)
     assert f[1] != g[1]
+    f.createIfcCartesianPoint((0.0, 0.0))
+    assert f[1] == f[1]
+    assert f[1] != f[2]
+
+
+def test_equality_of_owning_file():
+    f = ifcopenshell.file()
+    g = ifcopenshell.file()
+    f.createIfcCartesianPoint((0.0, 0.0))
+    f.createIfcCartesianPoint((0.0, 0.0))
+    g.createIfcCartesianPoint((0.0, 0.0))
+    assert f[1].file == f[1].file
+    assert f[1].file == f[2].file
+    assert f[1].file != g[1].file
 
 
 def test_setting_logical():