Send the available chat commands to clients which can show them

Adds the server side of the chat command list: a view plugin which
sends one ChatCommandInfo per available command, and the handler for
the request of a client which supports it.

Both are limited to the extended protocol, so classic clients don't
receive messages they can't understand. The commands come from
GetAvailableChatCommandInfos, so a player only learns about the ones
he may execute, and deactivated ones stay out.

Executing a command needs nothing new: the client sends the composed
command line as an ordinary chat message, which the chat message
processor already routes to the command without broadcasting it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MSpK6jkyF8ZS5nYXyGwYxA
(cherry picked from commit f3a9cb132c295863942bb0f06f40cde231e57907)

tests/MUnique.OpenMU.Tests/ChatCommandPacketTest.cs

@@ -0,0 +1,91 @@
+// <copyright file="ChatCommandPacketTest.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Tests;
+
+using MUnique.OpenMU.Network.Packets.ServerToClient;
+
+/// <summary>
+/// Tests for the packets which describe the chat commands.
+/// </summary>
+[TestFixture]
+public class ChatCommandPacketTest
+{
+    /// <summary>
+    /// Tests that the values of a command survive the way through the packet, so that
+    /// none of the fields overlaps another one.
+    /// </summary>
+    [Test]
+    public void ChatCommandInfoKeepsItsValues()
+    {
+        const int parameterCount = 3;
+        var data = new byte[ChatCommandInfoRef.GetRequiredSize(parameterCount)];
+
+        var written = new ChatCommandInfoRef(data)
+        {
+            Index = 7,
+            Count = 42,
+            MinimumCharacterStatus = CharacterStatus.GameMaster,
+            ParameterCount = parameterCount,
+            Command = "/item",
+            Name = "Item chat command",
+            Description = "Drops a specific item next to the character.",
+        };
+
+        var group = written[0];
+        group.Name = "Group";
+        group.ShortName = "group";
+        group.IsRequired = true;
+        group.Type = ChatCommandInfo.ChatCommandParameterType.Number;
+
+        var ancient = written[1];
+        ancient.Name = "Ancient";
+        ancient.ShortName = "anc";
+        ancient.ValidValues = "0|1|2";
+        ancient.Type = ChatCommandInfo.ChatCommandParameterType.Number;
+
+        var skill = written[2];
+        skill.Name = "Skill";
+        skill.ShortName = "sk";
+        skill.Type = ChatCommandInfo.ChatCommandParameterType.Boolean;
+
+        var read = new ChatCommandInfoRef(data);
+
+        Assert.That(read.Header.Code, Is.EqualTo(0xF5));
+        Assert.That(read.Header.SubCode, Is.EqualTo(0x01));
+        Assert.That(read.Index, Is.EqualTo(7));
+        Assert.That(read.Count, Is.EqualTo(42));
+        Assert.That(read.MinimumCharacterStatus, Is.EqualTo(CharacterStatus.GameMaster));
+        Assert.That(read.ParameterCount, Is.EqualTo(parameterCount));
+        Assert.That(read.Command, Is.EqualTo("/item"));
+        Assert.That(read.Name, Is.EqualTo("Item chat command"));
+        Assert.That(read.Description, Is.EqualTo("Drops a specific item next to the character."));
+
+        Assert.That(read[0].Name, Is.EqualTo("Group"));
+        Assert.That(read[0].ShortName, Is.EqualTo("group"));
+        Assert.That(read[0].IsRequired, Is.True);
+        Assert.That(read[0].ValidValues, Is.Empty);
+
+        Assert.That(read[1].Name, Is.EqualTo("Ancient"));
+        Assert.That(read[1].ShortName, Is.EqualTo("anc"));
+        Assert.That(read[1].ValidValues, Is.EqualTo("0|1|2"));
+        Assert.That(read[1].IsRequired, Is.False);
+
+        Assert.That(read[2].Name, Is.EqualTo("Skill"));
+        Assert.That(read[2].Type, Is.EqualTo(ChatCommandInfo.ChatCommandParameterType.Boolean));
+    }
+
+    /// <summary>
+    /// Tests that the size grows by exactly one parameter entry, so that the parameters
+    /// don't overlap the fields before them.
+    /// </summary>
+    [Test]
+    public void ChatCommandInfoSizeDependsOnParameterCount()
+    {
+        var withoutParameters = ChatCommandInfoRef.GetRequiredSize(0);
+        var withOneParameter = ChatCommandInfoRef.GetRequiredSize(1);
+
+        Assert.That(withOneParameter - withoutParameters, Is.EqualTo(ChatCommandInfo.ChatCommandParameter.Length));
+    }
+}