test(client): pin 1.7.0 backend_metrics shape with deterministic structural assertions

[Muawiya-contact]

test(client): pin 1.7.0 backend_metrics shape with deterministic structural assertions

Closes #326

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What does this PR do?

Replaces the loose assertGreater(len(...), 1) check in test_metric.py with deterministic structural assertions based on the actual /metrics/backend response captured from a real HugeGraph server.

The problem

The old assertion only checked length — shape drift in the API response would pass silently without any test failure.

# Before — too loose
self.assertGreater(len(backend_metrics["hugegraph"]), 1)

The fix

# After — deterministic structural assertion
missing_keys = EXPECTED_BACKEND_SERVER_KEYS - set(server_entry.keys())
self.assertFalse(missing_keys, f"Missing expected keys: {missing_keys}")

What was verified

• Captured the actual /metrics/backend response from a real HugeGraph server
• Pinned EXPECTED_BACKEND_SERVER_KEYS from that real response
• Asserts backend, nodes, cluster_id, servers fields exist with correct types
• Asserts all expected rocksdb metric keys are present in the server entry

Test results

Server version	Result
HugeGraph 1.7.0 (Docker)	✅ PASSED
HugeGraph latest (Docker)	✅ PASSED

Both versions return identical shapes — one assertion covers both.

Files changed

Only one file touched: hugegraph-python-client/src/tests/api/test_metric.py

[Muawiya-contact]

@imbajin, any feedback please?