Add more safeguards to prevent RUNNINGBOARD 0xdead10cc crashes

This commit adds more safeguards to prevent RUNNINGBOARD 0xdead10cc
crashes, by:
1. Using the `beginBackgroundTask(withName:expirationHandler:)` to
   request additional background execution time before completely
   suspending the app. See https://developer.apple.com/documentation/xcode/sigkill
2. Reorganizing app closing/cleanup tasks to be done in parallel when
   possible to decrease time needed to cleanup resources.

Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damus/ContentView.swift

@@ -513,9 +513,21 @@ struct ContentView: View {
             switch phase {
             case .background:
                 print("txn: 📙 DAMUS BACKGROUNDED")
+                let bgTask = this_app.beginBackgroundTask(withName: "Closing things down gracefully", expirationHandler: { [weak damus_state] in
+                    Log.error("App background signal handling: RUNNING OUT OF TIME! JUST CLOSE NDB DIRECTLY!", for: .app_lifecycle)
+                    // Background time about to expire, so close ndb directly.
+                    // This may still cause a memory error crash if subscription tasks have not been properly closed yet, but that is less likely than a 0xdead10cc crash if we don't do anything here.
+                    damus_state?.ndb.close()
+                })
+                
                 damusClosingTask = Task { @MainActor in
+                    Log.debug("App background signal handling: App being backgrounded", for: .app_lifecycle)
+                    let startTime = CFAbsoluteTimeGetCurrent()
                     await damus_state.nostrNetwork.close()  // Close ndb streaming tasks before closing ndb to avoid memory errors
+                    Log.debug("App background signal handling: Nostr network closed after %.2f seconds", for: .app_lifecycle, CFAbsoluteTimeGetCurrent() - startTime)
                     damus_state.ndb.close()
+                    Log.debug("App background signal handling: Ndb closed after %.2f seconds", for: .app_lifecycle, CFAbsoluteTimeGetCurrent() - startTime)
+                    this_app.endBackgroundTask(bgTask)
                 }
                 break
             case .inactive:

damus/Core/Networking/NostrNetworkManager/NostrNetworkManager.swift

@@ -61,9 +61,18 @@ class NostrNetworkManager {
     }
     
     func close() async {
+        await withTaskGroup { group in
+            // Spawn each cancellation task in parallel for faster execution speed
+            group.addTask {
                 await self.reader.cancelAllTasks()
+            }
+            group.addTask {
                 await self.profilesManager.stop()
+            }
             pool.close()
+            // But await on each one to prevent race conditions
+            for await value in group { continue }
+        }
     }
     
     func ping() {

damus/Core/Networking/NostrNetworkManager/ProfilesManager.swift

@@ -42,6 +42,7 @@ extension NostrNetworkManager {
                     try await Task.sleep(for: .seconds(1))
                     try Task.checkCancellation()
                     if subscriptionNeedsUpdate {
+                        try Task.checkCancellation()
                         self.restartProfileListenerTask()
                         subscriptionNeedsUpdate = false
                     }
@@ -50,11 +51,20 @@ extension NostrNetworkManager {
         }
         
         func stop() async {
-            self.subscriptionSwitcherTask?.cancel()
-            self.profileListenerTask?.cancel()
+            await withTaskGroup { group in
+                // Spawn each cancellation in parallel for better execution speed
+                group.addTask {
+                    await self.subscriptionSwitcherTask?.cancel()
                     try? await self.subscriptionSwitcherTask?.value
+                }
+                group.addTask {
+                    await self.profileListenerTask?.cancel()
                     try? await self.profileListenerTask?.value
                 }
+                // But await for all of them to be done before returning to avoid race conditions
+                for await value in group { continue }
+            }
+        }
         
         private func restartProfileListenerTask() {
             self.profileListenerTask?.cancel()
@@ -70,6 +80,7 @@ extension NostrNetworkManager {
             let pubkeys = Array(streams.keys)
             guard pubkeys.count > 0 else { return }
             let profileFilter = NostrFilter(kinds: [.metadata], authors: pubkeys)
+            try Task.checkCancellation()
             for await ndbLender in self.subscriptionManager.streamIndefinitely(filters: [profileFilter], streamMode: .ndbFirst) {
                 try Task.checkCancellation()
                 try? ndbLender.borrow { ev in

damus/Core/Networking/NostrNetworkManager/SubscriptionManager.swift

@@ -387,15 +387,24 @@ extension NostrNetworkManager {
             }
             
             func cancelAllTasks() async {
+                await withTaskGroup { group in
                     Log.info("Cancelling all SubscriptionManager tasks", for: .subscription_manager)
+                    // Start each task cancellation in parallel for faster execution
                     for (taskId, _) in self.tasks {
                         Log.info("Cancelling SubscriptionManager task %s", for: .subscription_manager, taskId.uuidString)
-                    await cancelAndCleanUp(taskId: taskId)
+                        group.addTask {
+                            await self.cancelAndCleanUp(taskId: taskId)
+                        }
+                    }
+                    // However, wait until all cancellations are complete to avoid race conditions.
+                    for await value in group {
+                        continue
                     }
                     Log.info("Cancelled all SubscriptionManager tasks", for: .subscription_manager)
                 }
             }
         }
+    }
     
     enum StreamItem {
         /// An event which can be borrowed from NostrDB

damus/Shared/Utilities/Log.swift

@@ -14,6 +14,7 @@ enum LogCategory: String {
     case render
     case storage
     case networking
+    case app_lifecycle
     case subscription_manager
     case timeline
     /// Logs related to Nostr Wallet Connect components