OAuth Support (#53)

Rips out the old auth method, adds OAuth support. Fixes #51.

Tested Platforms:
- [x] Linux
    - [x] Flatpak
    - [x] Native (Nix)
- [x] Android
- [ ] Windows
- [ ] MacOS

Reviewed-on: Nexus/nexus#53

lib/models/requests/get_event.dart

@@ -2,9 +2,8 @@ import "package:freezed_annotation/freezed_annotation.dart";
 part "get_event.freezed.dart";
 part "get_event.g.dart";
 
-@Freezed()
+@freezed
 abstract class GetEventRequest with _$GetEventRequest {
-  const GetEventRequest._();
   const factory GetEventRequest({
     required String roomId,
     required String eventId,