fix(hct626_dual_watertimer): follow file naming convention

legacy_type added to provide backward compatibility

custom_components/tuya_local/devices/HCT-626_dual_water_timer.yaml → custom_components/tuya_local/devices/hct626_dual_watertimer.yaml

@@ -1,4 +1,5 @@
 name: Dual water timer
+legacy_type: HCT-626_dual_water_timer
 products:
   - id: smd9kj1n
     model: HCT-626