Refactor JSON serialization and simplify enum handling

Simplified `GameType` enum in `CreateGameRequest.cs` by removing conditional compilation and redundant `JsonConverter` attributes. Compatibility with .NET 7 is no longer required.

Author: christiannagel

src/clients/Codebreaker.GameAPIs.Client/GamesClient.cs

@@ -215,7 +215,6 @@ public async Task<IEnumerable<GameInfo>> GetGamesAsync(GamesQuery query, Cancell
     }
 }
 
-
 [JsonSourceGenerationOptions(WriteIndented = true, PropertyNameCaseInsensitive = true)]
 [JsonSerializable(typeof(CreateGameRequest))]
 [JsonSerializable(typeof(CreateGameResponse))]
@@ -232,4 +231,4 @@ public async Task<IEnumerable<GameInfo>> GetGamesAsync(GamesQuery query, Cancell
 internal partial class GamesClientJsonContext : JsonSerializerContext
 {
 
-}
+}

src/clients/Codebreaker.GameAPIs.Client/Models/CreateGameRequest.cs

@@ -5,11 +5,7 @@ namespace Codebreaker.GameAPIs.Client.Models;
 /// <summary>
 /// The list of possible game types
 /// </summary>
-#if NET8_0_OR_GREATER
 [JsonConverter(typeof(JsonStringEnumConverter<GameType>))]
-#else
-[JsonConverter(typeof(JsonStringEnumConverter))]
-#endif
 public enum GameType
 {
     Game6x4,