MSC4075 Use expirationTS to define the call ringing window (#4652)

* Listen to call decline to stop ringing when declined from other device

* MSC4075 Use expirationTS to define the call ringing window

* Implement ElementCallService tests.

* Update acknowledgements.

ElementX/Sources/Mocks/CXProviderMock.swift

@@ -0,0 +1,17 @@
+//
+// Copyright 2025 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+//
+
+extension CXProviderMock {
+    struct Configuration { }
+    
+    convenience init(_ configuration: Configuration) {
+        self.init()
+        reportNewIncomingCallWithUpdateCompletionClosure = { _, _, completion in
+            completion(nil)
+        }
+    }
+}