add invite blocking support plus msc4494 support

To accomplish this I also reworked how account data is stored and added a method to fetch capabilities, and another method to set account data

lib/models/spec_versions_response.dart

@@ -0,0 +1,25 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+part "spec_versions_response.freezed.dart";
+part "spec_versions_response.g.dart";
+
+@freezed
+abstract class SpecVersionsResponse with _$SpecVersionsResponse {
+  const factory SpecVersionsResponse({
+    required IList<String> versions,
+    required UnstableFeatures unstableFeatures,
+  }) = _SpecVersionsResponse;
+
+  factory SpecVersionsResponse.fromJson(Map<String, Object?> json) =>
+      _$SpecVersionsResponseFromJson(json);
+}
+
+@freezed
+abstract class UnstableFeatures with _$UnstableFeatures {
+  const factory UnstableFeatures({
+    @JsonKey(name: "uk.timedout.msc4494") @Default(false) bool msc4494,
+  }) = _UnstableFeatures;
+
+  factory UnstableFeatures.fromJson(Map<String, Object?> json) =>
+      _$UnstableFeaturesFromJson(json);
+}