fix: ios skip posting hash response after detached from engine (#22695)

* skip posting message after detached from engine

* review changes

* cancel plugin before destroying engine

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/ios/Runner/Core/ImmichPlugin.swift

@@ -0,0 +1,17 @@
+class ImmichPlugin: NSObject {
+  var detached: Bool
+  
+  override init() {
+    detached = false
+    super.init()
+  }
+  
+  func detachFromEngine() {
+    self.detached = true
+  }
+  
+  func completeWhenActive<T>(for completion: @escaping (T) -> Void, with value: T) {
+    guard !self.detached else { return }
+    completion(value)
+  }
+}