Mi Band 6: Enable World clock setting

Also take care of new/old firmware

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/huami/miband6/MiBand6Coordinator.java

@@ -70,6 +70,16 @@ public class MiBand6Coordinator extends HuamiCoordinator {
         return true;
     }
 
+    @Override
+    public int getWorldClocksSlotCount() {
+        return 20; // as enforced by Mi Fit
+    }
+
+    @Override
+    public int getWorldClocksLabelLength() {
+        return 30; // at least
+    }
+
     @Override
     public int[] getSupportedDeviceSpecificSettings(GBDevice device) {
         return new int[]{
@@ -78,6 +88,7 @@ public class MiBand6Coordinator extends HuamiCoordinator {
                 R.xml.devicesettings_custom_emoji_font,
                 R.xml.devicesettings_timeformat,
                 R.xml.devicesettings_dateformat,
+                R.xml.devicesettings_world_clocks,
                 R.xml.devicesettings_nightmode,
                 R.xml.devicesettings_liftwrist_display_sensitivity,
                 R.xml.devicesettings_swipeunlock,

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/huami/HuamiSupport.java

@@ -978,7 +978,7 @@ public class HuamiSupport extends AbstractBTLEDeviceSupport {
             return;
         }
 
-        writeToChunked2021(builder, (short) 0x0008, getNextHandle(), baos.toByteArray(), false, false);
+        writeToChunked2021(builder, (short) 0x0008, getNextHandle(), baos.toByteArray(), force2021Protocol, false);
     }
 
     public byte[] encodeWorldClock(final WorldClock clock) {