Patched (temporarily) the DocC documentation (#8)

This PR contains the work done to:
* Documented the public properties, initializers, and/or functions of those types conforming to the `APIClient`, `KeyNameFilter`, and `KeyNameModel` protocols, to fix the issue that the protocol documentations cannot be inherited;
* Moved the `AmiiboService` DocC documentation catalog inside the library target;
* Amended the folder structure of the library and test targets;
* Fixed further documentation issues encountered while revising the written documentation;
* Added the `lib-test` task in the `Makefile` file;
* Improved the naming for the existing tasks in the `Makefile` file.

Reviewed-on: #8
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

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

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===
+//
+// This source file is part of the AmiiboService open source project
+//
+// Copyright (c) 2024-2025 Röck+Cöde VoF. and the AmiiboAPI project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of AmiiboAPI project authors
+//
+//===----------------------------------------------------------------------===
+
+extension Amiibo {
+    /// A model that represents the usage of an amiibo item within a certain game.
+    public struct Usage: Sendable {
+        
+        // MARK: Properties
+        
+        /// An explanation of how to use an amiibo item.
+        public let explanation: String
+        
+        /// A flag that indicates whether an amiibo item can save game data in it.
+        public let isWriteable: Bool
+        
+        // MARK: Initializers
+
+        /// Initializes this model from a given payload.
+        /// - Parameter payload: A payload that contains the values for the model.
+        init(_ payload: Components.Schemas.AmiiboUsage) {
+            self.explanation = payload.Usage
+            self.isWriteable = payload.write
+        }
+        
+    }
+}