examples: add ctr-example (#295)

Add very basic example of running a Linux container using
Containerization

Signed-off-by: Eric Ernst <eric_ernst@apple.com>

examples/ctr-example/Sources/ctr-example/main.swift

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Containerization project authors. All rights reserved.
+//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import Containerization
+import ContainerizationOS
+import Foundation
+
+@main
+struct CtrExample {
+    static func main() async throws {
+        print("Starting container example...")
+
+        // Set up terminal in raw mode (like cctl)
+        let current = try Terminal.current
+        try current.setraw()
+        defer { current.tryReset() }
+
+        // Create container manager with file-based initfs
+        var manager = try await ContainerManager(
+            kernel: Kernel(path: URL(fileURLWithPath: "./vmlinux"), platform: .linuxArm),
+            initfsReference: "vminit:latest",
+            network: try ContainerManager.VmnetNetwork()
+        )
+
+        let containerId = "ctr-example"
+        let imageReference = "docker.io/library/alpine:3.16"
+
+        print("Creating container from \(imageReference)...")
+
+        // Create container with simple configuration
+        let container = try await manager.create(
+            containerId,
+            reference: imageReference,
+            rootfsSizeInBytes: 1.gib()
+        ) { @Sendable config in
+            config.cpus = 2
+            config.memoryInBytes = 512.mib()
+            config.process.setTerminalIO(terminal: current)
+            config.process.arguments = ["/bin/sh"]
+            config.process.workingDirectory = "/"
+        }
+
+        // Clean up on exit
+        defer {
+            try? manager.delete(containerId)
+        }
+
+        print("Starting container...")
+        try await container.create()
+        try await container.start()
+
+        // Resize terminal to match current window
+        try? await container.resize(to: try current.size)
+
+        // Wait for container to finish
+        let exitCode = try await container.wait()
+
+        print("Container exited with code \(exitCode)")
+        try await container.stop()
+    }
+}