feat(ecostrad_iqceramicv2_radiator): add power, voltage and current sensors (#6297)
Adds power, voltage and current sensors to the Ecostrad iQ Ceramic v2
config, using previously unmapped dps:
- 118: voltage (V × 10)
- 119: power (W × 10)
- 120: current (mA)
These aren't in the cloud data model, so I worked the meanings out from
the values. Tested on my own heater while it was heating:
```
{"1": true, "3": 300, "32": "heating", "118": 2292, "119": 16868, "120": 6907, "121": 20}
```
That gives 229.2 V, 1686.8 W and 6.907 A. The heater reads 0 W / 0 A
when off. Volts × amps comes out within a few percent of the reported
power across several readings, and the other user's logs in #4799 fit
the same scales.
All three are marked optional. Dp 121 (always 20) is still unmapped.
AI-assisted: I've reviewed the change and tested it on my own Home
Assistant install.
Jon Wood