Implement node validation and improve merging logic
- Added `validateIncomingNode` function to validate new nodes against existing nodes, checking for public key conflicts and ensuring proper handling of node updates.
- Updated `nodeDBFactory` to utilize the new validation function when adding nodes.
- Enhanced `getNodes` method to optionally include the current node in the results.
- Removed the `mergeNodeInfo` utility as its functionality is now integrated into the validation and merging process.
- Updated tests to cover new validation logic and ensure correct behavior during node addition and merging.
- Cleaned up unused utility functions related to key comparison.
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