chore: migrate deprecation code && code cleanup (#708)

Fixes all issues in `flutter analyze`.
<Reviewed>

Commits:
* chore: migrate deprecated text style

* chore: migrate `toggleableActiveColor` to individual theme

* chore: don't use 'BuildContext's across async gaps

lib/ui/views/contributors/contributors_view.dart

@@ -23,7 +23,7 @@ class ContributorsView extends StatelessWidget {
                 child: Text(
                   '',
                   style: GoogleFonts.inter(
-                    color: Theme.of(context).textTheme.headline6!.color,
+                    color: Theme.of(context).textTheme.titleLarge!.color,
                   ),
                 ),
               ),