chore: add Option type (#26467)

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>

mobile/lib/utils/option.dart

@@ -0,0 +1,58 @@
+sealed class Option<T> {
+  const Option();
+
+  const factory Option.some(T value) = Some<T>;
+
+  const factory Option.none() = None<T>;
+
+  factory Option.fromNullable(T? value) => value != null ? Some(value) : None<T>();
+
+  @pragma('vm:prefer-inline')
+  bool get isSome => this is Some<T>;
+
+  @pragma('vm:prefer-inline')
+  bool get isNone => this is None<T>;
+
+  @pragma('vm:prefer-inline')
+  T? get unwrapOrNull => switch (this) {
+    Some(:final value) => value,
+    None() => null,
+  };
+
+  U fold<U>(U Function(T value) onSome, U Function() onNone) => switch (this) {
+    Some(:final value) => onSome(value),
+    None() => onNone(),
+  };
+
+  @override
+  String toString() => switch (this) {
+    Some(:final value) => 'Some($value)',
+    None() => 'None',
+  };
+}
+
+final class Some<T> extends Option<T> {
+  final T value;
+
+  const Some(this.value);
+
+  @override
+  bool operator ==(Object other) => other is Some<T> && other.value == value;
+
+  @override
+  int get hashCode => value.hashCode;
+}
+
+final class None<T> extends Option<T> {
+  const None();
+
+  @override
+  bool operator ==(Object other) => other is None<T>;
+
+  @override
+  int get hashCode => 0;
+}
+
+extension ObjectOptionExtension<T> on T? {
+  Option<T> toOption() => Option.fromNullable(this);
+}