Swift 6 migration for NSE (#5608)

* swift 6 support for NSE and concurrency safe implementations for it

* enforcing required Sendable conformance for swift 6 migration in NSE

* use Mutex to access the string builder cache

* use an async stream to update timeline items diffs

* fix for Sendable appHooks

ElementX/Sources/Other/Extensions/Bundle.swift

@@ -7,6 +7,7 @@
 //
 
 import Foundation
+import Synchronization
 
 public extension Bundle {
     /// The top-level bundle that contains the entire app.
@@ -24,12 +25,12 @@ public extension Bundle {
     
     // MARK: - Localisation
     
-    /// Overrides `Bundle.app.preferredLocalizations` for testing translations.
-    static var overrideLocalizations: [String]?
-    
-    private static let cacheDispatchQueue = DispatchQueue(label: "io.element.elementx.localization_bundle_cache")
-    private static var cachedBundles = [String: Bundle]()
-    
+    /// Overrides `Bundle.app.preferredLocalizations` for testing translations since this is
+    /// only for testing, and is changed at runtime only in tests, it's fine to keep as `nonisolated(unsafe)`
+    nonisolated(unsafe) static var overrideLocalizations: [String]?
+
+    private static let cachedBundles = Mutex<[String: Bundle]>([:])
+
     /// Get an lproj language bundle from the receiver bundle.
     /// - Parameter language: The language to try to load.
     /// - Returns: The lproj bundle if found otherwise nil.
@@ -37,32 +38,25 @@ public extension Bundle {
         if let bundle = cachedValue(forKey: language) {
             return bundle
         }
-        
+
         guard let lprojURL = Bundle.app.url(forResource: language, withExtension: "lproj") else {
             return nil
         }
-        
+
         let bundle = Bundle(url: lprojURL)
-        
+
         cacheValue(bundle, forKey: language)
-        
+
         return bundle
     }
-    
+
     // MARK: - Private
-    
+
     private static func cacheValue(_ value: Bundle?, forKey key: String) {
-        cacheDispatchQueue.sync {
-            cachedBundles[key] = value
-        }
+        cachedBundles.withLock { $0[key] = value }
     }
-    
+
     private static func cachedValue(forKey key: String) -> Bundle? {
-        var result: Bundle?
-        cacheDispatchQueue.sync {
-            result = cachedBundles[key]
-        }
-        
-        return result
+        cachedBundles.withLock { $0[key] }
     }
 }