RegisterCopierChannelLenMetric creates and registers the copier channel len metric with a callback that should return the length of the channel.

FlushSize defines the batch size.

Keep these const values in pgmodel/metrics to avoid cyclic import since 'trace' may also need this.

Keep these const values in pgmodel/metrics to avoid cyclic import since 'trace' may also need this.

MaxSentTs is the max timestamp sent to the database.