Add data directory lock status query builder

[Will-thom]

Summary

• Add a Memgraph query builder method for DATA DIRECTORY LOCK STATUS.
• Expose a top-level data_directory_lock_status helper/class.
• Document and test that the query uses execute_and_fetch.

Fixes #253

Tests

• Targeted pytest for data_directory_lock_status tests passed.
• Black check passed for touched Python files.

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