feat: Remove custom JSON converters for enums (#32)

Co-authored-by: SergeyMenshykh <sergemenshikh@gmail.com>

Author: stephentoub

src/A2A/KebabCaseLowerJsonStringEnumConverter.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace A2A;
+
+/// <summary>
+/// A JSON string enum converter that converts enum values to kebab-case lower strings.
+/// </summary>
+/// <typeparam name="TEnum">The type of the enum to convert.</typeparam>
+[EditorBrowsable(EditorBrowsableState.Never)]
+public sealed class KebabCaseLowerJsonStringEnumConverter<TEnum>() :
+    JsonStringEnumConverter<TEnum>(JsonNamingPolicy.KebabCaseLower)
+    where TEnum : struct, Enum;

src/A2A/Models/Message.cs

@@ -6,7 +6,7 @@ namespace A2A;
 /// <summary>
 /// Message sender's role.
 /// </summary>
-[JsonConverter(typeof(MessageRoleConverter))]
+[JsonConverter(typeof(KebabCaseLowerJsonStringEnumConverter<MessageRole>))]
 public enum MessageRole
 {
     /// <summary>

src/A2A/Models/TaskState.cs

@@ -5,7 +5,7 @@ namespace A2A;
 /// <summary>
 /// Represents the possible states of a Task.
 /// </summary>
-[JsonConverter(typeof(TaskStateJsonConverter))]
+[JsonConverter(typeof(KebabCaseLowerJsonStringEnumConverter<TaskState>))]
 public enum TaskState
 {
     /// <summary>