feat: Moves core functionality into it's own library.

Sources/CliDocCore/Builder.swift

@@ -0,0 +1,73 @@
+@resultBuilder
+public enum TextBuilder {
+
+  @inlinable
+  public static func buildPartialBlock<N: TextNode>(first: N) -> N {
+    first
+  }
+
+  @inlinable
+  public static func buildPartialBlock<N0: TextNode, N1: TextNode>(accumulated: N0, next: N1) -> NodeContainer {
+    .init(nodes: [accumulated, next])
+  }
+
+  @inlinable
+  public static func buildArray<N: TextNode>(_ components: [N]) -> NodeContainer {
+    .init(nodes: components)
+  }
+
+  @inlinable
+  public static func buildBlock<N: TextNode>(_ components: N...) -> NodeContainer {
+    .init(nodes: components)
+  }
+
+  @inlinable
+  public static func buildEither<N: TextNode, N1: TextNode>(first component: N) -> EitherNode<N, N1> {
+    .first(component)
+  }
+
+  @inlinable
+  public static func buildEither<N: TextNode, N1: TextNode>(second component: N1) -> EitherNode<N, N1> {
+    .second(component)
+  }
+
+  @inlinable
+  public static func buildOptional<N: TextNode>(_ component: N?) -> N? {
+    component
+  }
+
+}
+
+public enum EitherNode<N: TextNode, N1: TextNode>: TextNode {
+  case first(N)
+  case second(N1)
+
+  public var body: some TextNode {
+    switch self {
+    case let .first(node): return node.eraseToAnyTextNode()
+    case let .second(node): return node.eraseToAnyTextNode()
+    }
+  }
+}
+
+public struct NodeContainer: TextNode {
+
+  @usableFromInline
+  var nodes: [any TextNode]
+
+  @usableFromInline
+  init(nodes: [any TextNode]) {
+    self.nodes = nodes.reduce(into: [any TextNode]()) { array, next in
+      if let many = next as? NodeContainer {
+        array += many.nodes
+      } else {
+        array.append(next)
+      }
+    }
+  }
+
+  @inlinable
+  public var body: some TextNode {
+    nodes.reduce("") { $0 + $1.render() }
+  }
+}