feat: add get_lineage() to Python client

[psaikaushik]

Summary\n\nAdds the missing get_lineage(node_id, depth) method to the Python client, allowing users to fetch the lineage graph for any node directly from Python without resorting to raw curl calls.\n\nCloses #1798 (Python client portion)\n\n## What Changed\n\nAdded MarquezClient.get_lineage() that calls GET /api/v1/lineage?nodeId=<nodeId>&depth=<depth>.\n\nThe method follows the same patterns as existing client methods:\n- Input validation (node_id must not be None)\n- Uses DEFAULT_DEPTH (20) when depth is not specified\n- Returns the parsed JSON response\n\n## Usage\n\npython\nfrom marquez_client import MarquezClient\n\nclient = MarquezClient(url='http://localhost:8080')\n\n# Get lineage for a dataset\nlineage = client.get_lineage('dataset:my_namespace:my_dataset')\n\n# Get lineage for a job with custom depth\nlineage = client.get_lineage('job:my_namespace:my_job', depth=5)\n\n\n## Note\n\nThis PR covers the Python client. The Java client portion of #1798 will be a separate PR.\n\n## Checklist\n- [x] Follows existing client patterns\n- [x] Includes docstring with node_id format examples\n- [x] Input validation for required parameters

[boring-cyborg]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.18%. Comparing base (180f37b) to head (53eef39).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #3101   +/-   ##
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  Coverage     81.18%   81.18%           
  Complexity     1506     1506           
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  Files           268      268           
  Lines          7356     7356           
  Branches        325      325           
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  Hits           5972     5972           
  Misses         1226     1226           
  Partials        158      158           

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[psaikaushik]

Closing in favor of #3104 which fixes the PR description formatting and includes DCO sign-off.