feat: Implement IRC Gateway Service and related functionality

- Add IrcGatewayService to handle IRC connections and commands.
- Create IrcMessage class for parsing IRC protocol lines.
- Implement IrcMessageFormatter for formatting messages as IRC lines.
- Define IrcNumericReply constants for IRC numeric replies.
- Add IrcOptions class for configuration settings related to IRC.
- Create IrcServiceExtensions for adding IRC services to the application.
- Refactor ChannelsController to use IChatService for broadcasting messages and channel updates.
- Update ChatHub to utilize IChatService for user connection and message handling.
- Introduce ChatService to manage chat-related operations and interactions.
- Implement SignalRBroadcaster for broadcasting messages to SignalR clients.
- Update PresenceTracker to retrieve usernames for connections.
- Modify appsettings.example.json to include IRC configuration options.
- Update solution file to include the new IRC project.

src/EchoHub.Server.Irc/IrcServiceExtensions.cs

@@ -0,0 +1,26 @@
+using EchoHub.Core.Contracts;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace EchoHub.Server.Irc;
+
+public static class IrcServiceExtensions
+{
+    public static WebApplicationBuilder AddIrcGateway(this WebApplicationBuilder builder)
+    {
+        builder.Services.Configure<IrcOptions>(
+            builder.Configuration.GetSection(IrcOptions.SectionName));
+
+        if (builder.Configuration.GetValue<bool>("Irc:Enabled"))
+        {
+            builder.Services.AddSingleton<IrcGatewayService>();
+            builder.Services.AddSingleton<IChatBroadcaster>(sp =>
+                new IrcBroadcaster(sp.GetRequiredService<IrcGatewayService>()));
+            builder.Services.AddHostedService(sp =>
+                sp.GetRequiredService<IrcGatewayService>());
+        }
+
+        return builder;
+    }
+}