feat: Working on node builder

Sources/CliDoc/Nodes/Group.swift

@@ -1,4 +1,3 @@
-
 public struct Group: NodeRepresentable {
   @usableFromInline
   let node: any NodeRepresentable
@@ -25,10 +24,10 @@ public struct Group: NodeRepresentable {
 
   @inlinable
   public init(
-    separator: AnyNode = Space().eraseToAnyNode(),
+    separator: String = " ",
     @NodeBuilder _ build: () -> any NodeRepresentable
   ) {
-    self.init(separator: separator, node: build())
+    self.init(separator: separator.eraseToAnyNode(), node: build())
   }
 
   @inlinable