test(sdk-core): fix collection weight tests to actually verify weight changes

The tests "should update collection adding weights to existing items" and
"should update collection removing weights from items" were only checking that
the update payload was correct, but weren't actually verifying that the weight
properties were added or removed from the items.

This patch fixes both tests to explicitly verify:
- Adding weights: checks that itemWeight properties are present with correct values
- Removing weights: checks that itemWeight properties are absent

Without this fix, the tests could pass even if the implementation didn't
actually modify the weight properties, providing false confidence in the
functionality.

Co-authored-by: Claude Code <noreply@anthropic.com>

Author: aspiers

packages/sdk-core/tests/repository/HypercertOperationsImpl.test.ts

@@ -1382,6 +1382,12 @@ describe("HypercertOperationsImpl", () => {
           }),
         }),
       );
+
+      // Explicitly verify that itemWeight was added to both items
+      const putRecordCall = mockAgent.com.atproto.repo.putRecord.mock.calls[0][0];
+      const updatedItems = putRecordCall.record.items;
+      expect(updatedItems[0]).toHaveProperty("itemWeight", "30");
+      expect(updatedItems[1]).toHaveProperty("itemWeight", "70");
     });
 
     it("should update collection removing weights from items", async () => {