feat: add multiplayer session support with ENet host/join

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerAlreadyConnectedException.cs

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+namespace Game.Features.Multiplayer.Contracts.Exceptions;
+
+/// <summary>
+/// Thrown when trying to host or join while already connected to a session.
+/// </summary>
+public sealed class MultiplayerAlreadyConnectedException() : MultiplayerException("Already connected to a session.");

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerAlreadyConnectedException.cs.uid

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+uid://dr6f5t6nhh60w

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerAlreadyHostingException.cs

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+namespace Game.Features.Multiplayer.Contracts.Exceptions;
+
+/// <summary>
+/// Thrown when trying to host or join while already hosting a session.
+/// </summary>
+public sealed class MultiplayerAlreadyHostingException() : MultiplayerException("Already hosting a session.");

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerAlreadyHostingException.cs.uid

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+uid://c41cffks8ymh0

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerException.cs

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+using System;
+
+namespace Game.Features.Multiplayer.Contracts.Exceptions;
+
+/// <summary>
+/// Base type for multiplayer connection failures.
+/// </summary>
+public abstract class MultiplayerException(string message) : Exception(message);

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerException.cs.uid

@@ -0,0 +1 @@
+uid://ct5t3i77ovfx1

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerHostException.cs

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+namespace Game.Features.Multiplayer.Contracts.Exceptions;
+
+/// <summary>
+/// Thrown when starting a host fails at the transport level.
+/// </summary>
+public sealed class MultiplayerHostException(int port, string reason)
+    : MultiplayerException($"Failed to start host on port {port}: {reason}.")
+{
+    public int Port { get; } = port;
+    public string Reason { get; } = reason;
+}

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerHostException.cs.uid

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+uid://scqi785gvntu

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerJoinException.cs

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+namespace Game.Features.Multiplayer.Contracts.Exceptions;
+
+/// <summary>
+/// Thrown when connecting to a host fails at the transport level.
+/// </summary>
+public sealed class MultiplayerJoinException(string address, int port, string reason)
+    : MultiplayerException($"Failed to connect to {address}:{port}: {reason}.")
+{
+    public string Address { get; } = address;
+    public int Port { get; } = port;
+    public string Reason { get; } = reason;
+}

src/Features/Multiplayer/Contracts/Exceptions/MultiplayerJoinException.cs.uid

@@ -0,0 +1 @@
+uid://q8oyea00yrxy