test(asset-management): fix flaky import assets test (unique temp dir) [DX-9770]

makeSpaceDir() used `am-test-${Date.now()}`, which collided when two tests ran within
the same millisecond, so one test's asset index leaked into another's space dir. That
intermittently made resolveAssetsChunkedLocation find an index in the 'empty space' test,
skipping the empty-space branch and flaking expect(tickStub.callCount).to.equal(1)
(seen as 'expected +0 to equal 1'). Use fsReal.mkdtempSync for a guaranteed-unique dir.
Verified: 8/8 consecutive runs now 242 passing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NbgqgVDTDmh6c9LwDtMEf9

Author: netrajpatel

packages/contentstack-asset-management/test/unit/import/assets.test.ts

@@ -33,7 +33,11 @@ describe('ImportAssets', () => {
   afterEach(() => sinon.restore());
 
   const makeSpaceDir = () => {
-    const dir = path.join(os.tmpdir(), `am-test-${Date.now()}`);
+    // mkdtempSync guarantees a unique dir. Using `am-test-${Date.now()}` collided when two
+    // tests ran within the same millisecond, letting one test's asset index leak into
+    // another — which intermittently skipped the "empty space" branch and flaked the
+    // tick-count assertion.
+    const dir = fsReal.mkdtempSync(path.join(os.tmpdir(), 'am-test-'));
     fsReal.mkdirSync(path.join(dir, 'assets'), { recursive: true });
     return dir;
   };