Make distributionByTariff data available as totalCost value is not accurate with TimeOfUse

The API totalCost value does not accurately represent the actual cost where time-of-use tarrifs are in use. Evnex describe this as a legacy value, one that appears to use a single tariff where that tariff lacks precision. In Home Assitant time-of-use tariff's can be added in a template as an example and with totalEnergyUsage we can calculate a more accurate cost. Except where there is a mix of solar and grid energy, as we don't know the mix of grid and solar energy. However this is contained in the get session response.

"totalEnergyUsage": {
"total": 1041.0,
"distributionByTariff": { -- If these values could be surfaced we could work out the true cost ourselves
"solar": 88.9, -- either including solar export as a percieved cost or just a zero value.
"flat": 11.1
},
"distributionByEnergySource": {
"cogeneration": 0.1,
"gas": 0.1,
"geothermal": 2.4,
"hydro": 7,
"localSolar": 88.9,
"solar": 0.2,
"wind": 1.3
}
},
"totalCost": {
"currency": "NZD",
"amount": 0.0348, -- This is not a correct value where time of use tariffs are used.
"distribution": {
"flat": 100
}

I am going to attempt this myself, but I am not a Dev so raising it here as a backstop.

Regards

Start by locating the get session response handling and the existing totalEnergyUsage and totalCost fields. Trace how response data is represented and exposed, then make totalEnergyUsage.distributionByTariff available alongside the other usage values. Done means callers can access the tariff distribution from a session response without relying on the inaccurate totalCost value.

Written by the indexing model from the issue text.