Introduce mock SDK timeline items and a live, lorem ipsum based, timeline provider

ElementX/Sources/Mocks/RoomTimelineProviderMock.swift

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+//
+// Copyright 2024 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Combine
+import Foundation
+import MatrixRustSDK
+
+@MainActor
+class AutoUpdatingRoomTimelineProviderMock: RoomTimelineProvider {
+    private let innerUpdatePublisher: PassthroughSubject<[TimelineDiff], Never>
+    private let innerPaginationStatePublisher: PassthroughSubject<PaginationState, Never>
+    private let innerItems: [TimelineItemProxy] = []
+    
+    init() {
+        innerUpdatePublisher = .init()
+        innerPaginationStatePublisher = .init()
+        
+        super.init(currentItems: [],
+                   isLive: true,
+                   updatePublisher: innerUpdatePublisher.eraseToAnyPublisher(),
+                   paginationStatePublisher: innerPaginationStatePublisher.eraseToAnyPublisher())
+        
+        Task.detached { [weak self] in
+            for _ in 0...100 {
+                try? await Task.sleep(for: .seconds(1))
+                
+                let diff = TimelineDiffSDKMock()
+                diff.changeReturnValue = .append
+                diff.appendReturnValue = [TimelineItemFixtures.messageTimelineItem]
+                
+                self?.innerUpdatePublisher.send([diff])
+            }
+        }
+    }
+}