better loading indicators for timetables, talk and files

lib/api/requestCache.dart

@@ -15,6 +15,15 @@ abstract class RequestCache<T extends ApiResponse?> {
 
   int maxCacheTime;
   void Function(T)? onUpdate;
+
+  /// Called only when [start] finds a cached payload in localstore. Use this
+  /// (instead of [onUpdate]) when callers need to distinguish stale-but-fast
+  /// cache hits from authoritative network responses.
+  void Function(T)? onCacheData;
+
+  /// Called only when [start] receives a fresh payload from the network.
+  void Function(T)? onNetworkData;
+
   void Function(Exception) onError;
   bool? renew;
 
@@ -26,7 +35,14 @@ abstract class RequestCache<T extends ApiResponse?> {
   /// attempt have settled.
   Future<void> get ready => _ready.future;
 
-  RequestCache(this.maxCacheTime, this.onUpdate, {this.onError = ignore, this.renew = false});
+  RequestCache(
+    this.maxCacheTime,
+    this.onUpdate, {
+    this.onError = ignore,
+    this.renew = false,
+    this.onCacheData,
+    this.onNetworkData,
+  });
 
   static void ignore(Exception e) {}
 
@@ -34,7 +50,9 @@ abstract class RequestCache<T extends ApiResponse?> {
     try {
       final tableData = await Localstore.instance.collection(collection).doc(document).get();
       if (tableData != null) {
-        onUpdate?.call(onLocalData(tableData['json']));
+        final cached = onLocalData(tableData['json']);
+        onUpdate?.call(cached);
+        onCacheData?.call(cached);
       }
 
       if (DateTime.now().millisecondsSinceEpoch - (maxCacheTime * 1000) < (tableData?['lastupdate'] ?? 0)) {
@@ -44,6 +62,7 @@ abstract class RequestCache<T extends ApiResponse?> {
       try {
         final newValue = await onLoad();
         onUpdate?.call(newValue);
+        onNetworkData?.call(newValue);
         Localstore.instance.collection(collection).doc(document).set({
           'json': jsonEncode(newValue),
           'lastupdate': DateTime.now().millisecondsSinceEpoch,