feat(studio): real install progress in the store dialog and the wizard

Both surfaces showed an indeterminate spinner for the whole install,
because the hub only offered a unary call. They now follow
HubAdmin/InstallModuleStream:

- The store's install dialog shows the phase in plain language, the
  overall percentage, megabytes while the size is known, and a seconds
  counter. The counter is the second, independent signal: it keeps
  running even if the hub goes quiet, which is what tells 'slow' apart
  from 'stuck'.
- The setup wizard shows the same bar per module instead of a spinner
  inside the button.
- New strings in both locales for the phases, the byte line and the
  elapsed counter.

progress_bar_visual_test writes the four waiting states to
build/progress/ in either theme, so the result can be judged without
launching the desktop app. Writing it turned up a real trap worth
recording: awaiting toImage() directly in a widget test leaves the
binding waiting forever - the file passed in six seconds, then sat
there until the ten-minute timeout failed the whole suite.
tester.runAsync() is the fix. Full suite: 186 passed.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_localizations_de.dart

@@ -1089,6 +1089,28 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get storeInstallProgressBody => 'Holen, verifizieren, entpacken…';
 
+  @override
+  String get installPhaseResolve => 'Modul wird gesucht';
+
+  @override
+  String get installPhaseDownload => 'Wird heruntergeladen';
+
+  @override
+  String get installPhaseInstall => 'Wird geprüft und entpackt';
+
+  @override
+  String get installPhaseDone => 'Fertig';
+
+  @override
+  String installBytes(String done, String total) {
+    return '$done von $total MB';
+  }
+
+  @override
+  String installElapsed(int seconds) {
+    return '$seconds s vergangen';
+  }
+
   @override
   String get storeLoadDocs => 'Dokumentation laden';