feat(net): D.2b-B B-Wire — PrivateUpdatePropertyInt (0x02CD) parser

Mirror of PublicUpdatePropertyInt (0x02CE) but with no guid field —
targets the local player's own object. Burden (EncumbranceVal, PropertyInt 5)
changes ride this opcode on every pick-up / drop. Layout: opcode(4) + seq(1)
+ property(4) + value(4) = 13 bytes. 3 tests: happy path, wrong opcode, truncated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/PrivateUpdatePropertyInt.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Buffers.Binary;
+
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Inbound <c>PrivateUpdatePropertyInt (0x02CD)</c> — the server updates one
+/// <c>PropertyInt</c> on the player's OWN object. Unlike the sibling
+/// <see cref="PublicUpdatePropertyInt"/> (0x02CE), this carries NO guid (it
+/// implicitly targets the local player). Burden (<c>EncumbranceVal</c>, PropertyInt 5)
+/// changes ride this opcode on every pick-up / drop.
+///
+/// <para>Wire layout (ACE <c>GameMessagePrivateUpdatePropertyInt</c>):</para>
+/// <code>
+///   u32 opcode = 0x02CD
+///   u8  sequence    // single byte (ByteSequence) — not honored, latest-wins (DR-4)
+///   u32 property    // PropertyInt enum
+///   i32 value
+/// </code>
+/// </summary>
+public static class PrivateUpdatePropertyInt
+{
+    public const uint Opcode = 0x02CDu;
+
+    public readonly record struct Parsed(uint Property, int Value);
+
+    /// <summary>Parse a raw 0x02CD body. Returns null on opcode mismatch / truncation.</summary>
+    public static Parsed? TryParse(ReadOnlySpan<byte> body)
+    {
+        if (body.Length < 13) return null;          // 4 + 1 + 4 + 4
+        if (BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode) return null;
+        int pos = 4;
+        pos += 1;                                   // sequence byte (not honored)
+        uint prop = BinaryPrimitives.ReadUInt32LittleEndian(body[pos..]); pos += 4;
+        int value = BinaryPrimitives.ReadInt32LittleEndian(body[pos..]);
+        return new Parsed(prop, value);
+    }
+}