Tweaks on top of #1775

Make new interface not have default methods, make `Shadow` body throw
and tiny style changes

src/main/java/carpet/fakes/BlockPistonBehaviourInterface.java

@@ -15,14 +15,10 @@ public interface BlockPistonBehaviourInterface {
     /**
      * @return whether this block is sticky in any way when moved by pistons
      */
-    default boolean isSticky(BlockState state) {
-        return false;
-    }
+    boolean isSticky(BlockState state);
 
     /**
      * @return whether the neighboring block is pulled along if this block is moved by pistons
      */
-    default boolean isStickyToNeighbor(Level level, BlockPos pos, BlockState state, BlockPos neighborPos, BlockState neighborState, Direction dir, Direction moveDir) {
-        return false;
-    }
+    boolean isStickyToNeighbor(Level level, BlockPos pos, BlockState state, BlockPos neighborPos, BlockState neighborState, Direction dir, Direction moveDir);
 }

src/main/java/carpet/mixins/ChestBlock_customStickyMixin.java

@@ -1,9 +1,9 @@
 package carpet.mixins;
 
-import carpet.fakes.BlockPistonBehaviourInterface;
 import org.spongepowered.asm.mixin.Mixin;
 
 import carpet.CarpetSettings;
+import carpet.fakes.BlockPistonBehaviourInterface;
 
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;

src/main/java/carpet/mixins/PistonStructureResolver_customStickyMixin.java

@@ -19,12 +19,14 @@ import net.minecraft.world.level.block.piston.PistonStructureResolver;
 import net.minecraft.world.level.block.state.BlockState;
 
 @Mixin(PistonStructureResolver.class)
-public abstract class PistonStructureResolver_customStickyMixin {
+public class PistonStructureResolver_customStickyMixin {
 
     @Shadow @Final private Level level;
     @Shadow @Final private Direction pushDirection;
 
-    @Shadow private static boolean canStickToEachOther(BlockState blockState, BlockState blockState2) { return false; }
+    @Shadow private static boolean canStickToEachOther(BlockState blockState, BlockState blockState2) {
+        throw new AssertionError();
+    }
 
     @Inject(
         method = "isSticky",
@@ -34,7 +36,7 @@ public abstract class PistonStructureResolver_customStickyMixin {
         )
     )
     private static void isSticky(BlockState state, CallbackInfoReturnable<Boolean> cir) {
-        if(state.getBlock() instanceof BlockPistonBehaviourInterface behaviourInterface){
+        if (state.getBlock() instanceof BlockPistonBehaviourInterface behaviourInterface){
             cir.setReturnValue(behaviourInterface.isSticky(state));
         }
     }