[KV] Add RocksDB Memory Metrics by Component Type

[platinumhamburg]

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• I searched in the issues and found nothing similar.

Motivation

Currently, Fluss only provides a total RocksDB memory usage metric (rocksdbMemoryUsageTotal) at the server level. This makes it difficult to diagnose memory issues or optimize RocksDB configuration. Users need visibility into individual memory components to:

• Identify memory bottlenecks (e.g., memtable vs block cache)
• Tune RocksDB configuration parameters appropriately
• Monitor write pressure through memtable metrics
• Track read cache effectiveness through block cache metrics

Solution

Add detailed RocksDB memory metrics to monitor memory usage breakdown by component type. These metrics are aggregated at the table level (TableMetricGroup) and help users understand which RocksDB components consume the most memory.

Anything else?

No response

Willingness to contribute

• I'm willing to submit a PR!