Support for bidirectional energy entities

[alistairmackenzie]

When monitoring a battery circuit where the battery charges on a time-of-use tariff, the energy is subtracted from the value during the expensive periods. This is somewhat desirable for net-metering scenarios with solar; however, it does not seem particularly valuable with batteries. This issue also occurs with mixed-use bidirectional circuits.

Image showing energy in both directions from Home Assistant:

This is seen when using a FiftyAmpBidirectional channel type.

One ideal solution would be to have a separate entity tracking the return power. This would also allow users to use Emporia data in Home Assistant's energy dashboard, which requires an entity for in-energy and out-energy.

I suspect this would also provide a solution to #334, as users could choose the return entity for solar tracking.

I'm happy to provide any data, etc, to support this feature if required. I've already tried implementing it myself. However, my knowledge of Home Assistant's internals is severely lacking