Encapsulates idle connection pruning logic for ChannelDbConnectionPool. Periodically samples the idle connection count and, once enough samples are collected, computes the median and prunes that many idle connections from the pool.

This type is only instantiated when the pool can shrink (MinPoolSize < MaxPoolSize) and idle-timeout based reclamation is enabled (Connection Idle Timeout > 0). When the pool is fixed-size or idle reclamation is disabled, the pool holds no PoolPruner instance.