chore: import upstream snapshot with attribution

Sources/ContainerizationExtras/NetworkConfiguration.swift

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 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 network interface's addresses.
+public struct InterfaceAddress: Sendable, Hashable {
+    public var ipv4Address: CIDRv4
+    public var ipv6Address: CIDRv6?
+
+    public init(ipv4Address: CIDRv4, ipv6Address: CIDRv6? = nil) {
+        self.ipv4Address = ipv4Address
+        self.ipv6Address = ipv6Address
+    }
+}
+
+/// A link-scoped route — a destination directly reachable on an interface.
+public struct LinkRoute: Sendable, Hashable {
+    public var ipv4Destination: IPv4Address?
+    public var ipv4Source: IPv4Address?
+    public var ipv6Destination: IPv6Address?
+    public var ipv6Source: IPv6Address?
+
+    public init(
+        ipv4Destination: IPv4Address? = nil,
+        ipv4Source: IPv4Address? = nil,
+        ipv6Destination: IPv6Address? = nil,
+        ipv6Source: IPv6Address? = nil
+    ) {
+        self.ipv4Destination = ipv4Destination
+        self.ipv4Source = ipv4Source
+        self.ipv6Destination = ipv6Destination
+        self.ipv6Source = ipv6Source
+    }
+}
+
+/// The default-route gateway for a network interface.
+public struct DefaultRoute: Sendable, Hashable {
+    public var ipv4Gateway: IPv4Address?
+    public var ipv6Gateway: IPv6Address?
+
+    public init(ipv4Gateway: IPv4Address? = nil, ipv6Gateway: IPv6Address? = nil) {
+        self.ipv4Gateway = ipv4Gateway
+        self.ipv6Gateway = ipv6Gateway
+    }
+}