Updated Foundation import to use only essentials on Linux

Author: dimitribouniol

Sources/WebPush/Push Message/Notification.swift

@@ -6,7 +6,11 @@
 //  Copyright © 2024-25 Mochi Development, Inc. All rights reserved.
 //
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 // MARK: - Notification
 

Sources/WebPush/Push Message/PushMessage.swift

@@ -6,7 +6,5 @@
 //  Copyright © 2024-25 Mochi Development, Inc. All rights reserved.
 //
 
-import Foundation
-
 /// Common Push Message types.
 public enum PushMessage: Sendable {}