Fix persisted-nodes gauge

[jait91]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates the SMTNodesPersistedTotal metric to track aggregator records (SMT leaves) from MongoDB instead of SMT nodes, which are stored in RocksDB. To support this, the EstimatedCount method was added to the AggregatorRecordStorage interface and implemented for MongoDB. Feedback suggests that adding this method to the interface may break existing mock implementations or alternative storage backends. Additionally, because the metric name aggregator_smt_nodes_persisted_total is now misleading, it is recommended to deprecate it in favor of a more accurately named metric.

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