Improve docs for ChannelUsage
Try to clarify more that the ChannelUsage is for describing the usage for one particular channel request, not for the channel as a whole. This is a potentially confusing point, so we should spell it out completely.
Try to clarify more that the ChannelUsage is for describing the usage for one particular channel request, not for the channel as a whole. This is a potentially confusing point, so we should spell it out completely.