Optimize diff algorithm

[Goooler]

Follow up #103.

        /**
         * Called to check whether two objects represent the same item.
         * <p>
         * For example, if your items have unique ids, this method should check their id equality.
         * <p>
         * Note: {@code null} items in the list are assumed to be the same as another {@code null}
         * item and are assumed to not be the same as a non-{@code null} item. This callback will
         * not be invoked for either of those cases.
         *
         * @param oldItem The item in the old list.
         * @param newItem The item in the new list.
         * @return True if the two items represent the same object or false if they are different.
         * @see Callback#areItemsTheSame(int, int)
         */
        public abstract boolean areItemsTheSame(@NonNull T oldItem, @NonNull T newItem);

        /**
         * Called to check whether two items have the same data.
         * <p>
         * This information is used to detect if the contents of an item have changed.
         * <p>
         * This method to check equality instead of {@link Object#equals(Object)} so that you can
         * change its behavior depending on your UI.
         * <p>
         * For example, if you are using DiffUtil with a
         * {@link RecyclerView.Adapter RecyclerView.Adapter}, you should
         * return whether the items' visual representations are the same.
         * <p>
         * This method is called only if {@link #areItemsTheSame(T, T)} returns {@code true} for
         * these items.
         * <p>
         * Note: Two {@code null} items are assumed to represent the same contents. This callback
         * will not be invoked for this case.
         *
         * @param oldItem The item in the old list.
         * @param newItem The item in the new list.
         * @return True if the contents of the items are the same or false if they are different.
         * @see Callback#areContentsTheSame(int, int)
         */
        public abstract boolean areContentsTheSame(@NonNull T oldItem, @NonNull T newItem);

[Goooler]

https://github.com/android/sunflower/blob/69472521b0e0dea9ffb41db223d6ee1cb27bd557/app/src/main/java/com/google/samples/apps/sunflower/adapters/GardenPlantingAdapter.kt#L79-L94