KIP-488 — Clean up Sum,Count,Total Metrics

Accepted Kafka 2.4 Metrics

Consolidates and renames the overlapping `Count`, `Sum`, `Total`, and `SampledTotal` metric classes in Kafka's metrics framework, eliminating redundant stat implementations and clarifying the semantics of cumulative vs. windowed counts. The existing metric hierarchy has multiple classes with confusingly similar names and behaviors, some of which are duplicates, making it difficult for developers to choose the right metric type.

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