feat: add terminal session lifecycle

- add replaceable terminal session abstraction

- manage terminal modes on start and stop

- route runtime and example through terminal session

src/Example/Program.cs

@@ -4,16 +4,14 @@ using TinyTUI.Input;
 using TinyTUI.Overlay;
 using TinyTUI.Rendering;
 using TinyTUI.Runtime;
-using TinyTUI.Stdio;
-using TinyTUI.Stdout;
+using TinyTUI.Terminal;
 using TinyTUI.Text;
 
-using var terminalInput = new ConsoleTerminalInput();
-var terminalOutput = new ConsoleTerminalOutput();
+using var terminal = new ConsoleTerminalSession();
 var parser = new DefaultInputParser();
 var textMeasurer = new TerminalTextMeasurer();
-var renderer = new DifferentialRenderer(terminalOutput, textMeasurer);
-using var runtime = new TuiRuntime(terminalInput, parser, renderer);
+var renderer = new DifferentialRenderer(terminal, textMeasurer);
+using var runtime = new TuiRuntime(terminal, parser, renderer);
 
 var done = new ManualResetEventSlim();
 var eventsText = new Text("最近事件:\n- 无");
@@ -109,7 +107,6 @@ AddAll(
 
 runtime.Add(page);
 runtime.SetFocus(input);
-terminalOutput.ShowCursor();
 
 var loaderTask = RunLoaderAsync(loader, runtime, loaderCancellation.Token);
 
@@ -122,9 +119,8 @@ finally
 {
     StopLoader(loaderCancellation, loaderTask);
     runtime.Stop();
-    terminalOutput.ShowCursor();
-    terminalOutput.Write("\r\n");
-    terminalOutput.Flush();
+    terminal.Write("\r\n");
+    terminal.Flush();
 }
 
 static async Task RunLoaderAsync(Loader loader, ITuiRuntime runtime, CancellationToken cancellationToken)