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/ifcwrap/IfcParseWrapper.i

@@ -263,13 +263,29 @@ private:
 %newobject ifcopenshell::file::create_uninitialized;
 
 %extend ifcopenshell::file {
-	/*
 	// Use to correlate to entity_instance.file_pointer, so that we
 	// can trace file ownership of instances on the python side.
 	size_t file_pointer() const {
 		return reinterpret_cast<size_t>($self);
 	}
-	*/
+
+	%pythoncode %{
+		def __eq__(self, other):
+			# Attribute access hands out a new wrapper every time, so identity
+			# of the wrapper says nothing about the file it refers to.
+			if self is other:
+				return True
+			if not isinstance(other, file):
+				return NotImplemented
+			return self.file_pointer() == other.file_pointer()
+
+		def __ne__(self, other):
+			result = self.__eq__(other)
+			return result if result is NotImplemented else not result
+
+		def __hash__(self):
+			return self.file_pointer()
+	%}
 
 	file(const std::string& schema) {
 		return new ifcopenshell::file(ifcopenshell::schema_by_name(schema));
@@ -552,12 +568,10 @@ private:
         return oss.str();
 	}
 
-	/*
-	// Just something to have a somewhat sensible value to hash
+	// Identifies the file owning this instance, zero when it has no owner.
 	size_t file_pointer() const {
-		return reinterpret_cast<size_t>($self->file_);
+		return reinterpret_cast<size_t>($self->file());
 	}
-	*/
 
 	unsigned get_argument_index(const std::string& a) const {
 		if ($self->declaration().as_entity()) {