Fix MetadataFields text field values being lost in SupaEmailAuth widget (Fixes #113) (#114)

* Fix metadata field value persistence in SupaEmailAuth widget

Implement == operator and hashCode getter in MetaDataField class
Update _SupaEmailAuthState to use MetaDataField.key as map key
Modify related methods to work with new map structure
Ensure consistent hashing and correct retrieval of TextEditingControllers
Resolve issue of losing metadata field values during widget lifecycle

This change prevents the loss of user input in custom metadata fields
by ensuring proper object equality and consistent map key usage.

* Remove unecessary equality operator override and hashcode getter.

Author: bcorman

lib/src/components/supa_email_auth.dart

@@ -125,7 +125,7 @@ class _SupaEmailAuthState extends State<SupaEmailAuth> {
   final _formKey = GlobalKey<FormState>();
   final _emailController = TextEditingController();
   final _passwordController = TextEditingController();
-  late final Map<MetaDataField, TextEditingController> _metadataControllers;
+  late final Map<String, TextEditingController> _metadataControllers;
 
   bool _isLoading = false;
 
@@ -142,7 +142,8 @@ class _SupaEmailAuthState extends State<SupaEmailAuth> {
   void initState() {
     super.initState();
     _metadataControllers = Map.fromEntries((widget.metadataFields ?? []).map(
-        (metadataField) => MapEntry(metadataField, TextEditingController())));
+        (metadataField) =>
+            MapEntry(metadataField.key, TextEditingController())));
   }
 
   @override
@@ -225,7 +226,7 @@ class _SupaEmailAuthState extends State<SupaEmailAuth> {
                 ...widget.metadataFields!
                     .map((metadataField) => [
                           TextFormField(
-                            controller: _metadataControllers[metadataField],
+                            controller: _metadataControllers[metadataField.key],
                             textInputAction:
                                 widget.metadataFields!.last == metadataField
                                     ? TextInputAction.done
@@ -423,8 +424,7 @@ class _SupaEmailAuthState extends State<SupaEmailAuth> {
   Map<String, dynamic> _resolveMetadataFieldsData() {
     return widget.metadataFields != null
         ? _metadataControllers.map<String, dynamic>(
-            (metaDataField, controller) =>
-                MapEntry(metaDataField.key, controller.text))
+            (key, controller) => MapEntry(key, controller.text))
         : <String, dynamic>{};
   }
 }