Implement integration tests

- Create a new target that contains the integration tests
- Implement three test plans: `AllTests`, `UnitTests`, `IntegrationTests`

Sources/Flare/Classes/Models/IAPError.swift

@@ -44,6 +44,30 @@ public enum IAPError: Swift.Error {
 
 extension IAPError {
     init(error: Swift.Error?) {
+        if #available(iOS 15.0, tvOS 15.0, macOS 12.0, watchOS 8.0, *) {
+            if let storeKitError = error as? StoreKitError {
+                self.init(storeKitError: storeKitError)
+            } else {
+                self.init(error)
+            }
+        } else {
+            self.init(error)
+        }
+    }
+
+    @available(iOS 15.0, tvOS 15.0, macOS 12.0, watchOS 8.0, *)
+    private init(storeKitError: StoreKit.StoreKitError) {
+        switch storeKitError {
+        case .unknown:
+            self = .unknown
+        case .userCancelled:
+            self = .paymentCancelled
+        default:
+            self = .with(error: storeKitError)
+        }
+    }
+
+    private init(_ error: Swift.Error?) {
         switch (error as? SKError)?.code {
         case .paymentNotAllowed:
             self = .paymentNotAllowed

Sources/Flare/Classes/Providers/RefundProvider/IRefundProvider.swift

@@ -15,6 +15,7 @@ protocol IRefundProvider {
         @available(macOS, unavailable)
         @available(watchOS, unavailable)
         @available(tvOS, unavailable)
+        @MainActor
         func beginRefundRequest(productID: String) async throws -> RefundRequestStatus
     #endif
 }

Sources/Flare/Classes/Providers/RefundProvider/RefundProvider.swift

@@ -75,6 +75,7 @@ extension RefundProvider: IRefundProvider {
         @available(macOS, unavailable)
         @available(watchOS, unavailable)
         @available(tvOS, unavailable)
+        @MainActor
         func beginRefundRequest(productID: String) async throws -> RefundRequestStatus {
             let windowScene = try systemInfoProvider.currentScene
             let transactionID = try await refundRequestProvider.verifyTransaction(productID: productID)