Declared the "Persistence" library in the Package file.

Package.swift

@@ -46,6 +46,10 @@ let package = Package(
             name: "Dependencies",
             dependencies: []
         ),
+        .target(
+            name: "Persistence",
+            dependencies: []
+        ),
         // MARK: Test targets
         .testTarget(
             name: "CommunicationsTests",
@@ -76,6 +80,13 @@ let package = Package(
             ],
             path: "Tests/Dependencies"
         ),
+        .testTarget(
+            name: "PersistenceTests",
+            dependencies: [
+                "Persistence"
+            ],
+            path: "Tests/Persistence"
+        ),
     ]
 )