feat(core): Add new matchers and improve negation messaging

test/test.diffOutput.ts

@@ -0,0 +1,32 @@
+import { tap, expect as tExpect } from '@push.rocks/tapbundle';
+import * as smartexpect from '../dist_ts/index.js';
+
+tap.test('diff-like output for object.toEqual mismatch', async () => {
+  const a = { x: 1, y: 2 };
+  const b = { x: 1, y: 3 };
+  try {
+    smartexpect.expect(a).object.toEqual(b);
+    throw new Error('Assertion did not throw');
+  } catch (err: any) {
+    const msg: string = err.message;
+    tExpect(msg.includes('Expected objects to be deeply equal')).toBeTrue();
+    tExpect(msg.includes('Received:')).toBeTrue();
+    tExpect(msg.includes('"y": 2')).toBeTrue();
+  }
+});
+
+tap.test('diff-like output for array.toContainEqual mismatch', async () => {
+  const arr = [{ id: 1 }, { id: 2 }];
+  const item = { id: 3 };
+  try {
+    smartexpect.expect(arr).array.toContainEqual(item);
+    throw new Error('Assertion did not throw');
+  } catch (err: any) {
+    const msg: string = err.message;
+    tExpect(msg.includes('Expected array to contain equal to')).toBeTrue();
+    tExpect(msg.includes('Received:')).toBeTrue();
+    tExpect(msg.includes('"id": 1')).toBeTrue();
+  }
+});
+
+export default tap.start();