Improve the Saddle API for Horses

Not all horses with Saddles have armor. This lets us break up the horses with saddles
and access their saddle state separately from an interface shared with Armor.

paper-api/src/main/java/org/bukkit/inventory/ArmoredHorseInventory.java

@@ -0,0 +1,22 @@
+package org.bukkit.inventory;
+
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+@NullMarked
+public interface ArmoredHorseInventory extends AbstractHorseInventory {
+
+    /**
+     * Gets the item in the horse's armor slot.
+     *
+     * @return the armor item
+     */
+    @Nullable ItemStack getArmor();
+
+    /**
+     * Sets the item in the horse's armor slot.
+     *
+     * @param stack the new item
+     */
+    void setArmor(@Nullable ItemStack stack);
+}

paper-api/src/main/java/org/bukkit/inventory/HorseInventory.java

@@ -5,20 +5,4 @@ import org.jetbrains.annotations.Nullable;
 /**
  * An interface to the inventory of a Horse.
  */
-public interface HorseInventory extends AbstractHorseInventory {
-
-    /**
-     * Gets the item in the horse's armor slot.
-     *
-     * @return the armor item
-     */
-    @Nullable
-    ItemStack getArmor();
-
-    /**
-     * Sets the item in the horse's armor slot.
-     *
-     * @param stack the new item
-     */
-    void setArmor(@Nullable ItemStack stack);
-}
+public interface HorseInventory extends AbstractHorseInventory, ArmoredHorseInventory {}

paper-api/src/main/java/org/bukkit/inventory/LlamaInventory.java

@@ -6,7 +6,7 @@ import org.jetbrains.annotations.Nullable;
 /**
  * An interface to the inventory of a {@link Llama}.
  */
-public interface LlamaInventory extends AbstractHorseInventory {
+public interface LlamaInventory extends SaddledHorseInventory {
 
     /**
      * Gets the item in the llama's decor slot.

paper-api/src/main/java/org/bukkit/inventory/SaddledHorseInventory.java

@@ -0,0 +1,7 @@
+package org.bukkit.inventory;
+
+import org.jspecify.annotations.NullMarked;
+
+@NullMarked
+public interface SaddledHorseInventory extends AbstractHorseInventory {
+}