Added package initializers to the Amiibo models for testing.

Sources/AmiiboService/Public/Models/Amiibo/Amiibo+Usage.swift

@@ -26,6 +26,12 @@ extension Amiibo {
         
         // MARK: Initializers
 
+        /// Initializes this model.
+        package init(explanation: String, isWriteable: Bool) {
+            self.explanation = explanation
+            self.isWriteable = isWriteable
+        }
+
         /// Initializes this model from a given payload.
         /// - Parameter payload: A payload that contains the values for the model.
         init(_ payload: Components.Schemas.AmiiboUsage) {