Create sessions through the user session manager

Sign-in now creates and stores its session through the
UserSessionManagerProtocol rather than the UserSessionStore, so the
AppCoordinator no longer holds the store.

- The manager forwards clientSessionDelegate and
  userSession(for:sessionDirectories:passphrase:) to its store. As with
  restoring, the new session isn't registered until the AppCoordinator
  adds it.
- AuthenticationService takes the manager, for both sign-in and soft
  logout.
- The store mock's configuration moves to the manager mock.

ElementX/Sources/Services/UserSession/UserSessionManager.swift

@@ -7,6 +7,7 @@
 
 import Combine
 import Foundation
+import MatrixRustSDK
 import OrderedCollections
 
 /// Owns the live session of every account signed in on this device, most recently active first.
@@ -37,6 +38,10 @@ final class UserSessionManager: UserSessionManagerProtocol {
         accounts.values.first ?? nil
     }
     
+    var clientSessionDelegate: ClientSessionDelegate {
+        userSessionStore.clientSessionDelegate
+    }
+    
     init(userSessionStore: UserSessionStoreProtocol, appSettings: AppSettings) {
         self.userSessionStore = userSessionStore
         self.appSettings = appSettings
@@ -79,6 +84,10 @@ final class UserSessionManager: UserSessionManagerProtocol {
         return .failure(.failedRestoringSessions)
     }
     
+    func userSession(for client: ClientProtocol, sessionDirectories: SessionDirectories, passphrase: Data) async -> Result<UserSessionProtocol, UserSessionStoreError> {
+        await userSessionStore.userSession(for: client, sessionDirectories: sessionDirectories, passphrase: passphrase)
+    }
+    
     func add(_ userSession: UserSessionProtocol) {
         let userID = userSession.clientProxy.userID