fix: scope EVC cumulative-energy big word order to GEN1 only

The order32="big" override on charge_added_cum (from wills106#2178) was
verified on an X3-EVC-11kW Gen1 (serial C311*, ARM v1.18): at the same
instant the input copy 0x10-0x11 read [0, 3] (high-word-first) while
its holding twin 0x619-0x61A read [3, 0] and decoded to the correct
0.3 kWh little-endian.

Issue wills106#2230 shows the opposite population: an X3-HAC 22kW Gen2
(ARM v2.03) follows the documented little order, so the global
override inflated its lifetime total by a factor of 65536
(322.6 kWh -> 21,141,913.6).

The definition is now split per generation: GEN1 keeps order32="big"
(hardware-verified), GEN2 returns to the documented default order.

Fixes wills106#2230 (word-order part).

Author: Bl00d-B0b

custom_components/solax_modbus/plugin_solax_ev_charger.py

@@ -1118,6 +1118,19 @@ def value_function_sync_rtc_evc(initval: Any, descr: Any, datadict: dict[str, An
         native_unit_of_measurement=UnitOfEnergy.KILO_WATT_HOUR,
         device_class=SensorDeviceClass.ENERGY,
         state_class=SensorStateClass.TOTAL_INCREASING,
+        allowedtypes=GEN1,
+    ),
+    SolaXEVChargerModbusSensorEntityDescription(
+        name="Charge Added - Cumulative",
+        key="charge_added_cum",
+        register=0x10,
+        register_type=REG_INPUT,
+        register_data_type=REGISTER_U32,
+        scale=0.1,
+        native_unit_of_measurement=UnitOfEnergy.KILO_WATT_HOUR,
+        device_class=SensorDeviceClass.ENERGY,
+        state_class=SensorStateClass.TOTAL_INCREASING,
+        allowedtypes=GEN2,
     ),
     SolaXEVChargerModbusSensorEntityDescription(
         name="Charge Added Total",