Cached avatar support (from Rust) (#633)

* loading a cached avatar at first, and then actually doing the request so that the avatar can still be displayed without connection

* improved the code

* fix + changelog

* policy on how to fetch the avatar url added

* code improvements

* addressed al PR comments

* improved the error handling

* improved the async task code

* fixed a typo

* fixed another typo

ElementX/Sources/Services/Client/ClientProxyProtocol.swift

@@ -24,7 +24,6 @@ enum ClientProxyCallback {
 }
 
 enum ClientProxyError: Error {
-    case failedRetrievingAvatarURL
     case failedRetrievingDisplayName
     case failedRetrievingAccountData
     case failedSettingAccountData
@@ -72,6 +71,8 @@ protocol ClientProxyProtocol: AnyObject, MediaLoaderProtocol {
 
     var homeserver: String { get }
 
+    var avatarURLPublisher: AnyPublisher<URL?, Never> { get }
+
     var restorationToken: RestorationToken? { get }
     
     var visibleRoomsSummaryProvider: RoomSummaryProviderProtocol? { get }
@@ -85,9 +86,9 @@ protocol ClientProxyProtocol: AnyObject, MediaLoaderProtocol {
     func roomForIdentifier(_ identifier: String) async -> RoomProxyProtocol?
     
     func loadUserDisplayName() async -> Result<String, ClientProxyError>
-        
-    func loadUserAvatarURL() async -> Result<URL, ClientProxyError>
-    
+
+    func loadUserAvatarURL() async
+
     func accountDataEvent<Content: Decodable>(type: String) async -> Result<Content?, ClientProxyError>
     
     func setAccountData<Content: Encodable>(content: Content, type: String) async -> Result<Void, ClientProxyError>