models/word_search: clean up json de/serialization

lib/models/word_search/word_search_match_span.dart

@@ -33,6 +33,7 @@ class WordSearchMatchSpan {
   Map<String, Object?> toJson() => {
     'spanType': spanType.toString().split('.').last,
     'index': index,
+    'subIndex': subIndex,
     'start': start,
     'end': end,
   };
@@ -43,12 +44,13 @@ class WordSearchMatchSpan {
           (e) => e.toString().split('.').last == json['spanType'],
         ),
         index: json['index'] as int,
+        subIndex: json['subIndex'] as int? ?? 0,
         start: json['start'] as int,
         end: json['end'] as int,
       );
 
   @override
-  int get hashCode => Object.hash(spanType, index, start, end);
+  int get hashCode => Object.hash(spanType, index, subIndex, start, end);
 
   @override
   bool operator ==(Object other) {
@@ -56,6 +58,7 @@ class WordSearchMatchSpan {
     return other is WordSearchMatchSpan &&
         other.spanType == spanType &&
         other.index == index &&
+        other.subIndex == subIndex &&
         other.start == start &&
         other.end == end;
   }

lib/models/word_search/word_search_sense.dart

@@ -81,7 +81,7 @@ class WordSearchSense {
     'dialects': dialects.map((e) => e.toJson()).toList(),
     'misc': misc.map((e) => e.toJson()).toList(),
     'info': info,
-    'languageSource': languageSource,
+    'languageSource': languageSource.map((e) => e.toJson()).toList(),
   };
 
   factory WordSearchSense.fromJson(Map<String, dynamic> json) =>

lib/models/word_search/word_search_xref_entry.dart

@@ -16,6 +16,8 @@ class WordSearchXrefEntry {
   final bool ambiguous;
 
   /// The result of the cross-reference, may or may not be included in the query.
+  ///
+  /// Be careful not to introduce circular references when using this field.
   final WordSearchResult? xrefResult;
 
   const WordSearchXrefEntry({
@@ -40,6 +42,10 @@ class WordSearchXrefEntry {
         ambiguous: json['ambiguous'] as bool,
         baseWord: json['baseWord'] as String,
         furigana: json['furigana'] as String?,
-        xrefResult: null,
+        xrefResult: json['xrefResult'] != null
+            ? WordSearchResult.fromJson(
+                Map<String, dynamic>.from(json['xrefResult'] as Map),
+              )
+            : null,
       );
 }