fix(B.5): handle PickupEvent 0xF74A so picked-up items despawn locally

ACE sends GameMessagePickupEvent (opcode 0xF74A) instead of
GameMessageDeleteObject (0xF747) for items removed via player pickup
(Player_Tracking.RemoveTrackedObject with fromPickup=true).

Without this handler, BuildPickUp succeeded server-side (item moved
into the player's container, retail observers saw it disappear), but
our local client kept rendering it on the ground because the despawn
message went to the unhandled-opcode bucket.

PickupEvent's wire body adds an objectPositionSequence field on top
of DeleteObject's layout, so the parser is its own type. The
downstream view-removal semantics are identical to DeleteObject, so
the dispatcher routes both opcodes into the same EntityDeleted event
via a small adapter.

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

@@ -0,0 +1,41 @@
+using System.Buffers.Binary;
+using AcDream.Core.Net.Messages;
+using Xunit;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+public sealed class PickupEventTests
+{
+    [Fact]
+    public void RejectsWrongOpcode()
+    {
+        Span<byte> body = stackalloc byte[12];
+        BinaryPrimitives.WriteUInt32LittleEndian(body, 0xDEADBEEFu);
+
+        Assert.Null(PickupEvent.TryParse(body));
+    }
+
+    [Fact]
+    public void RejectsTruncated()
+    {
+        Assert.Null(PickupEvent.TryParse(ReadOnlySpan<byte>.Empty));
+        Assert.Null(PickupEvent.TryParse(new byte[11]));
+    }
+
+    [Fact]
+    public void ParsesGuidAndSequences()
+    {
+        Span<byte> body = stackalloc byte[12];
+        BinaryPrimitives.WriteUInt32LittleEndian(body, PickupEvent.Opcode);
+        BinaryPrimitives.WriteUInt32LittleEndian(body.Slice(4), 0x80000727u);
+        BinaryPrimitives.WriteUInt16LittleEndian(body.Slice(8), 0x1234);
+        BinaryPrimitives.WriteUInt16LittleEndian(body.Slice(10), 0x5678);
+
+        var parsed = PickupEvent.TryParse(body);
+
+        Assert.NotNull(parsed);
+        Assert.Equal(0x80000727u, parsed!.Value.Guid);
+        Assert.Equal((ushort)0x1234, parsed.Value.InstanceSequence);
+        Assert.Equal((ushort)0x5678, parsed.Value.PositionSequence);
+    }
+}