feat(account): add available countries state

- Create AvailableCountriesState class to manage the state of available countries
- Define AvailableCountriesStatus enum for different state statuses
- Implement copyWith method for easy state modification
- Override props method for Equatable comparison

Author: fulleni

lib/account/bloc/available_countries_state.dart

@@ -0,0 +1,35 @@
+part of 'available_countries_bloc.dart';
+
+enum AvailableCountriesStatus { initial, loading, success, failure }
+
+class AvailableCountriesState extends Equatable {
+  const AvailableCountriesState({
+    this.status = AvailableCountriesStatus.initial,
+    this.availableCountries = const [],
+    this.error,
+  });
+
+  final AvailableCountriesStatus status;
+  final List<Country> availableCountries;
+  final String? error;
+
+  AvailableCountriesState copyWith({
+    AvailableCountriesStatus? status,
+    List<Country>? availableCountries,
+    String? error,
+    bool clearError = false,
+  }) {
+    return AvailableCountriesState(
+      status: status ?? this.status,
+      availableCountries: availableCountries ?? this.availableCountries,
+      error: clearError ? null : error ?? this.error,
+    );
+  }
+
+  @override
+  List<Object?> get props => [
+    status,
+    availableCountries,
+    error,
+  ];
+}