HDDS-12455. Merge the SimpleMockNodeManager with MockNodeManager

[Russole]

What changes were proposed in this pull request?

• Refactored MockNodeManager to properly handle decommission and maintenance states, resolving inconsistencies in nodeMap and NodeOperationalState handling between MockNodeManager and SimpleMockNodeManager.
• Ensured nodeMap as the single source of truth and kept it in sync with DatanodeDetails and persisted operational state.
• Aligned MockNodeManager behavior with SimpleMockNodeManager to ensure consistent node operational state transitions in tests.
• Added unit tests to verify setNodeOperationalState updates NodeStatus (including expiry) and throws NodeNotFoundException for unknown nodes.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-12455

How was this patch tested?

All existing GitHub CI checks passed, and the newly added unit tests passed successfully.