Add support for deserializing manually deserialized items, also add caller note

paper-api/src/main/java/org/bukkit/configuration/serialization/ConfigurationSerializable.java

@@ -1,6 +1,7 @@
 package org.bukkit.configuration.serialization;
 
 import java.util.Map;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 
 /**
@@ -30,8 +31,12 @@ public interface ConfigurationSerializable {
      * This class must provide a method to restore this class, as defined in
      * the {@link ConfigurationSerializable} interface javadocs.
      *
+     * nb: It is not intended for this method to be called directly, this will
+     * be called by the {@link ConfigurationSerialization} class.
+     *
      * @return Map containing the current state of this class
      */
     @NotNull
+    @ApiStatus.OverrideOnly
     public Map<String, Object> serialize();
 }