[Task] Upgrade CI HugeGraph server to 1.7 and adapt tests

[imbajin]

Background

The current python-client CI workflow still starts hugegraph/hugegraph:1.3.0 in .github/workflows/hugegraph-python-client.yml. The file already carries a TODO for upgrading the server version, and PR #318 had to add a compatibility gate around /metrics/system because the legacy server returns 500 there.

Task

Upgrade the HugeGraph server used by python-client CI to 1.7, then adapt the client tests and compatibility assumptions to the newer server behavior.

Scope

• Update the workflow image tag from 1.3.0 to 1.7.x in .github/workflows/hugegraph-python-client.yml.
• Revisit python-client integration tests that currently encode old-server behavior.
• Remove temporary compatibility gates once CI runs against the newer server version.
• Verify the latest client code paths against HugeGraph 1.7 responses and error handling.

Acceptance Criteria

• python-client CI runs against HugeGraph 1.7 successfully.
• tests reflect current server behavior instead of legacy 1.3.0 quirks.
• any required client-side adjustments for 1.7 are included and documented in the PR.

Notes

• Recent context: PR refactor: remove 'incubating' branding, update docs & packaging #318 (refactor: remove 'incubating' branding, update docs & packaging) exposed that the workflow is still pinned to an old server image.\n- If 1.7 introduces API or payload differences, please update the relevant tests first and then tighten the assertions around the new behavior.