chore: import upstream snapshot with attribution

Sources/ContainerizationExtras/ProgressEvent.swift

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization project authors.
+//
+// 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
+//
+//   https://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.
+//===----------------------------------------------------------------------===//
+
+/// A progress update event.
+public enum ProgressEvent: Sendable {
+    /// The possible values:
+    ///  - `add-items`: Increment the number of processed items by `value`.
+    ///  - `add-total-items`: Increment the total number of items to process by `value`.
+    ///  - `add-size`: Increment the size of processed items by `value`.
+    ///  - `add-total-size`: Increment the total size of items to process by `value`.
+    case addItems(Int)
+    case addTotalItems(Int)
+    case addSize(Int64)
+    case addTotalSize(Int64)
+
+    /// The event name.
+    public var event: String {
+        switch self {
+        case .addItems: "add-items"
+        case .addTotalItems: "add-total-items"
+        case .addSize: "add-size"
+        case .addTotalSize: "add-total-size"
+        }
+    }
+
+    /// The event value.
+    public var value: any Sendable {
+        switch self {
+        case .addItems(let value): value
+        case .addTotalItems(let value): value
+        case .addSize(let value): value
+        case .addTotalSize(let value): value
+        }
+    }
+}
+
+/// The progress update handler.
+public typealias ProgressHandler = @Sendable (_ events: [ProgressEvent]) async -> Void