feat(combat): port retail held weapon parenting

Select the default combat mode from ordered equipped objects so bows request missile stance. Parse CreateObject parent metadata and ParentEvent, then render held objects as separate children composed from setup holding locations and placement frames each animation tick.

tests/AcDream.Core.Net.Tests/Messages/ParentEventTests.cs

@@ -0,0 +1,40 @@
+using System.Buffers.Binary;
+using AcDream.Core.Net.Messages;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+public sealed class ParentEventTests
+{
+    [Fact]
+    public void TryParse_RetailWireOrder()
+    {
+        var body = new byte[24];
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(0, 4), ParentEvent.Opcode);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4, 4), 0x50000001u);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8, 4), 0x60000002u);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12, 4), 2u);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(16, 4), 3u);
+        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(20, 2), 0x1234);
+        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(22, 2), 0x5678);
+
+        var parsed = ParentEvent.TryParse(body);
+
+        Assert.NotNull(parsed);
+        Assert.Equal(0x50000001u, parsed.Value.ParentGuid);
+        Assert.Equal(0x60000002u, parsed.Value.ChildGuid);
+        Assert.Equal(2u, parsed.Value.ParentLocation);
+        Assert.Equal(3u, parsed.Value.PlacementId);
+        Assert.Equal((ushort)0x1234, parsed.Value.ParentInstanceSequence);
+        Assert.Equal((ushort)0x5678, parsed.Value.ChildPositionSequence);
+    }
+
+    [Fact]
+    public void TryParse_RejectsTruncationAndWrongOpcode()
+    {
+        Assert.Null(ParentEvent.TryParse(new byte[23]));
+
+        var body = new byte[24];
+        BinaryPrimitives.WriteUInt32LittleEndian(body, 0xF748u);
+        Assert.Null(ParentEvent.TryParse(body));
+    }
+}