Add Terminal.Gui fork as submodule with transparent color support
(Color.Transparent emitting CSI 39m/49m default bg/fg sequences).
Switch EchoHub.Client from NuGet to project reference.
Update Transparent theme to use real terminal transparency.
- Implemented IrcCommandHandlerTests to cover various IRC commands including PING, JOIN, PART, and authentication scenarios.
- Added IrcMessageFormatterTests to validate message formatting for different message types such as text, images, files, and audio.
- Created IrcMessageTests to ensure correct parsing of IRC messages and handling of various command formats.
- Introduced TestHelpers to facilitate testing with mock connections and streams, including a FakeChatService and FakeEncryptionService for simulating chat behavior.