feat(wdyk_2p63a_energy_meter): add leakage current sensor

dp 6 (phase a) has two additional bytes compared with b and c phases.
The extra two bytes appear to be leakage current.

Issue #6284

custom_components/tuya_local/devices/wdyk_2p63a_energy_meter.yaml

@@ -193,6 +193,18 @@ entities:
         class: measurement
         mapping:
           - scale: 1000
+  - entity: sensor
+    name: Leakage current
+    class: current
+    dps:
+      - id: 6
+        type: base64
+        optional: true
+        name: sensor
+        mask: "0000000000000000FFFF"
+        unit: mA
+        class: measurement
+
   - entity: sensor
     translation_key: voltage_x
     translation_placeholders: