feat: Working on node builder

Sources/CliDoc/Nodes/Header.swift

@@ -1,32 +1,45 @@
 @preconcurrency import Rainbow
 
-public struct Header: NodeRepresentable {
+public struct Header: NodeRepresentable, @unchecked Sendable {
 
   @usableFromInline
-  let node: Text
+  let node: any NodeRepresentable
 
   @usableFromInline
-  let styles: [Style]
+  let color: NamedColor?
+
+  @usableFromInline
+  let styles: [Style]?
+
+  @inlinable
+  public init(
+    @NodeBuilder _ build: () -> any NodeRepresentable
+  ) {
+    self.node = build()
+    self.color = nil
+    self.styles = nil
+  }
 
   @inlinable
   public init(
     _ text: String,
     color: NamedColor? = .yellow,
-    styles: [Style] = [.bold]
+    styles: [Style]? = [.bold]
   ) {
-    var text = Text(text)
-    if let color {
-      text = text.color(color)
-    }
-    self.node = text
+    self.color = color
+    self.node = Text(text)
     self.styles = styles
   }
 
   @inlinable
   public func render() -> String {
-    styles.reduce(node) { node, style in
-      node.style(style)
+    var node = node
+    if let color {
+      node = node.color(color)
     }
-    .render()
+    if let styles {
+      node = node.style(styles)
+    }
+    return node.render()
   }
 }