feat: implement I-9 and W-4 tax form handling with dedicated use cases and mappers

apps/mobile/packages/domain/lib/src/entities/profile/tax_form.dart

@@ -4,27 +4,26 @@ enum TaxFormType { i9, w4 }
 
 enum TaxFormStatus { notStarted, inProgress, submitted, approved, rejected }
 
-class TaxForm extends Equatable {
+abstract class TaxForm extends Equatable {
   final String id;
-  final TaxFormType type;
+  TaxFormType get type;
   final String title;
   final String? subtitle;
   final String? description;
   final TaxFormStatus status;
   final String? staffId;
-  final Map<String, dynamic>? formData;
+  final Map<String, dynamic> formData;
   final DateTime? createdAt;
   final DateTime? updatedAt;
 
   const TaxForm({
     required this.id,
-    required this.type,
     required this.title,
     this.subtitle,
     this.description,
     this.status = TaxFormStatus.notStarted,
     this.staffId,
-    this.formData,
+    this.formData = const {},
     this.createdAt,
     this.updatedAt,
   });
@@ -43,3 +42,37 @@ class TaxForm extends Equatable {
         updatedAt,
       ];
 }
+
+class I9TaxForm extends TaxForm {
+  const I9TaxForm({
+    required super.id,
+    required super.title,
+    super.subtitle,
+    super.description,
+    super.status,
+    super.staffId,
+    super.formData,
+    super.createdAt,
+    super.updatedAt,
+  });
+
+  @override
+  TaxFormType get type => TaxFormType.i9;
+}
+
+class W4TaxForm extends TaxForm {
+  const W4TaxForm({
+    required super.id,
+    required super.title,
+    super.subtitle,
+    super.description,
+    super.status,
+    super.staffId,
+    super.formData,
+    super.createdAt,
+    super.updatedAt,
+  });
+
+  @override
+  TaxFormType get type => TaxFormType.w4;
+}