KIP-818 — Introduce cache-size-bytes-total Task Level Metric

Discussion StreamsMetrics

Introduces a new task-level metric `cache-size-bytes-total` in Kafka Streams that tracks the number of bytes accumulated in the record cache for a given task. The analogous `input-buffer-bytes-total` task metric was added in KIP-770 but the cache-size counterpart was omitted, leaving a monitoring gap for memory usage at the task level.

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