Split K8sHelper, add WorkerProvisioner protocol, and add LinuxWorker … (#2110)

- Closes #2102.
- LinuxWorkerProvisioner sets up a kind-based node.
- Includes some test cleanups.

Co-authored-by: John Logan <john_logan@apple.com>

Sources/ContainerBuild/Builder.swift

@@ -108,7 +108,7 @@ public struct Builder: Sendable {
         }
 
         if let terminal = config.terminal {
-            _ = Task {
+            Task {
                 let winchHandler = AsyncSignalHandler.create(notify: [SIGWINCH])
                 let setWinch = { (rows: UInt16, cols: UInt16) in
                     var winch = ClientStream()