feat: 🎸 allow passing created gumtree node in DSL

core/src/main/kotlin/tw/xcc/gumtree/helper/GumTreeCreatorHelper.kt

@@ -14,36 +14,41 @@ internal annotation class GumTreeMarker
 internal class GumTreeBuilder(grammarName: String, label: String, pos: Int, length: Int) {
     private val root by lazy { GumTree(TreeType(grammarName), label, pos, length) }
 
-    fun child(
+    inline fun child(
         grammarName: String,
         label: String = "",
         pos: Int = -1,
         length: Int = -1,
         block: GumTreeBuilder.() -> Unit
-    ) {
+    ): GumTree {
         contract {
             callsInPlace(block, InvocationKind.EXACTLY_ONCE)
         }
 
         val child = GumTreeBuilder(grammarName, label, pos, length)
         child.block()
-        root.addChild(child.build())
+
+        val childTree = child.build()
+        root.addChild(childTree)
+        return childTree
     }
 
     fun child(
         grammarName: String,
         label: String = "",
         pos: Int = -1,
         length: Int = -1
-    ) {
-        root.addChild(GumTree(TreeType(grammarName), label, pos, length))
+    ): GumTree {
+        val childTree = GumTree(TreeType(grammarName), label, pos, length)
+        root.addChild(childTree)
+        return childTree
     }
 
     internal fun build(): GumTree = root
 }
 
 @OptIn(ExperimentalContracts::class)
-internal fun gumTree(
+internal inline fun gumTree(
     grammarName: String,
     label: String = "",
     pos: Int = -1,