chore: import upstream snapshot with attribution

Sources/ContainerizationExtras/AddressAllocator.swift

@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+// 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.
+//===----------------------------------------------------------------------===//
+
+/// Conforming objects can allocate and free various address types.
+public protocol AddressAllocator<AddressType>: Sendable {
+    associatedtype AddressType: Sendable
+
+    /// Allocate a new address.
+    func allocate() throws -> AddressType
+
+    /// Attempt to reserve a specific address.
+    func reserve(_ address: AddressType) throws
+
+    /// Free an allocated address.
+    func release(_ address: AddressType) throws
+
+    /// If no addresses are allocated, prevent future allocations and return true.
+    func disableAllocator() -> Bool
+}
+
+/// Errors that a type implementing AddressAllocator should throw.
+public enum AllocatorError: Swift.Error, CustomStringConvertible, Equatable {
+    case allocatorDisabled
+    case allocatorFull
+    case alreadyAllocated(_ address: String)
+    case invalidAddress(_ index: String)
+    case invalidArgument(_ msg: String)
+    case invalidIndex(_ index: Int)
+    case notAllocated(_ address: String)
+    case rangeExceeded
+
+    public var description: String {
+        switch self {
+        case .allocatorDisabled:
+            return "the allocator is shutting down"
+        case .allocatorFull:
+            return "no free indices are available for allocation"
+        case .alreadyAllocated(let address):
+            return "cannot choose already-allocated address \(address)"
+        case .invalidAddress(let address):
+            return "cannot create index using address \(address)"
+        case .invalidArgument(let msg):
+            return "invalid argument: \(msg)"
+        case .invalidIndex(let index):
+            return "cannot create address using index \(index)"
+        case .notAllocated(let address):
+            return "cannot free unallocated address \(address)"
+        case .rangeExceeded:
+            return "cannot create allocator that overflows maximum address value"
+        }
+    }
+}