feat: add terminal text measurer

- measure terminal display width for text and escape sequences

- truncate rendered lines to terminal columns

- add width and truncation examples

src/Example/Program.cs

@@ -5,14 +5,16 @@ using TinyTUI.Rendering;
 using TinyTUI.Runtime;
 using TinyTUI.Stdio;
 using TinyTUI.Stdout;
+using TinyTUI.Text;
 
 using var terminalInput = new ConsoleTerminalInput();
 var terminalOutput = new ConsoleTerminalOutput();
 var parser = new DefaultInputParser();
-var renderer = new FullScreenRenderer(terminalOutput);
+var textMeasurer = new TerminalTextMeasurer();
+var renderer = new FullScreenRenderer(terminalOutput, textMeasurer);
 using var runtime = new TuiRuntime(terminalInput, parser, renderer);
 
-var component = new EchoComponent(runtime);
+var component = new EchoComponent(runtime, textMeasurer);
 runtime.Add(component);
 runtime.SetFocus(component);
 
@@ -34,7 +36,7 @@ finally
 /// <summary>
 /// 用于手动验证 Runtime 的示例组件
 /// </summary>
-file sealed class EchoComponent(ITuiRuntime runtime) : IInputComponent
+file sealed class EchoComponent(ITuiRuntime runtime, ITextMeasurer textMeasurer) : IInputComponent
 {
     private readonly ManualResetEventSlim _done = new();
     private readonly List<string> _events = [];
@@ -54,6 +56,13 @@ file sealed class EchoComponent(ITuiRuntime runtime) : IInputComponent
             "- 调整窗口大小 验证 Resize 事件会进入焦点组件并触发重渲染",
             "- 按 Esc 退出",
             string.Empty,
+            "宽度示例:",
+            $"字符串 \"abc\" 的终端宽度 = {textMeasurer.GetWidth("abc")}",
+            $"字符串 \"中文\" 的终端宽度 = {textMeasurer.GetWidth("中文")}",
+            $"字符串 \"😀\" 的终端宽度 = {textMeasurer.GetWidth("😀")}",
+            $"截断前 \"abc中文😀xyz\" 的终端宽度 = {textMeasurer.GetWidth("abc中文😀xyz")}",
+            $"截断到 8 列后的结果 = \"{textMeasurer.Truncate("abc中文😀xyz", 8)}\"",
+            string.Empty,
             "最近事件:",
         };