DiNTS: missing graph-break regression test (follow-up to #9145) #9159

Describe the bug

Follow-up to #9145 (fixes #9144). Per @ericspod's review: the merged tests don't check the condition from the issue, and we'd want to assert graph count to be 1 and graph breaks to be 0.

test_dints_network.py has no dynamo coverage today — TestDintsTopologyCache tests the snapshot mechanism, not the zero-graph-break outcome, so a regression in the topology branches would land silently.

Expected behavior

A test in test_dints_network.py asserting (1, 0), guarded by torch._dynamo.is_dynamo_supported().