Add MessengerStop function wrapper

Sources/XXMessengerClient/Messenger/Functions/MessengerStop.swift

+import Foundation
+import XCTestDynamicOverlay
+import XXClient
+
+public struct MessengerStop {
+  public struct Wait: Equatable {
+    public init(
+      sleepInterval: TimeInterval = 1,
+      retries: Int = 10
+    ) {
+      self.sleepInterval = sleepInterval
+      self.retries = retries
+    }
+
+    public var sleepInterval: TimeInterval
+    public var retries: Int
+  }
+
+  public enum Error: Swift.Error {
+    case notLoaded
+    case timedOut
+  }
+
+  public var run: (Wait?) throws -> Void
+
+  public func callAsFunction(wait: Wait? = nil) throws -> Void {
+    try run(wait)
+  }
+}
+
+extension MessengerStop {
+  public static func live(_ env: MessengerEnvironment) -> MessengerStop {
+    MessengerStop { wait in
+      guard let cMix = env.cMix() else {
+        throw Error.notLoaded
+      }
+      guard cMix.networkFollowerStatus() == .running else {
+        return
+      }
+      try cMix.stopNetworkFollower()
+      guard let wait else { return }
+      var retries = wait.retries
+      var hasRunningProcesses = cMix.hasRunningProcesses()
+      while retries > 0 && hasRunningProcesses {
+        env.sleep(wait.sleepInterval)
+        hasRunningProcesses = cMix.hasRunningProcesses()
+        retries -= 1
+      }
+      if hasRunningProcesses {
+        throw Error.timedOut
+      }
+    }
+  }
+}
+
+extension MessengerStop {
+  public static let unimplemented = MessengerStop(
+    run: XCTUnimplemented("\(Self.self)")
+  )
+}