fix: resolve Copilot review comments

- Rename PacketTests class to PushPayloadTests
- Remove stale cref references to deleted Options type

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/Configuration/Option.cs

@@ -29,7 +29,6 @@ namespace GeneralUpdate.Core.Configuration
     ///     </para>
     /// </remarks>
     /// <seealso cref="Option{T}" />
-    /// <seealso cref="Options" />
     public class Option
     {
         /// <summary>
@@ -162,7 +161,6 @@ public override bool Equals(object? obj)
     /// </remarks>
     /// <seealso cref="Option" />
     /// <seealso cref="OptionValue{T}" />
-    /// <seealso cref="Options" />
     public sealed class Option<T> : Option
     {
         /// <summary>

tests/CoreTest/Configuration/PushPayloadTests.cs

@@ -6,7 +6,7 @@ namespace CoreTest.Configuration;
 /// AAAT unit tests for <see cref="PushPayload"/> — property defaults, set/get, JSON serialization attrs.
 /// Covers: all nullable bool?/int?/DateTime?/string? properties, null vs non-null, IsForcibly/IsFreeze tri-state.
 /// </summary>
-public class PacketTests
+public class PushPayloadTests
 {
     [Fact]
     public void Ctor_Default_AllPropertiesAreNullOrDefault()