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/IrcOptions.cs

@@ -0,0 +1,15 @@
+namespace EchoHub.Server.Irc;
+
+public sealed class IrcOptions
+{
+    public const string SectionName = "Irc";
+
+    public bool Enabled { get; set; }
+    public int Port { get; set; } = 6667;
+    public bool TlsEnabled { get; set; }
+    public int TlsPort { get; set; } = 6697;
+    public string? TlsCertPath { get; set; }
+    public string? TlsCertPassword { get; set; }
+    public string ServerName { get; set; } = "echohub";
+    public string? Motd { get; set; }
+}