feat: tree-structure-compose (LazyTree) + O(n) addChild cycle check

- New published module tree-structure-compose: a LazyTree composable for Compose
  Multiplatform (JVM/desktop, iOS, Wasm) with lazy rendering and expand/collapse.
- Fix an O(n^2) regression in addChild(): only walk ancestors for cycle detection
  when the child already has a subtree (a fresh leaf can never form a cycle), so
  building deep trees is O(n) again. Caught by the deep-chain stack-safety test on JS.
- README: Compose usage section; align all install snippets to 4.0.0.
- Version catalog: Compose Multiplatform + compose-compiler plugins.

Verified locally: JVM, JS(node), Wasm(node), iOS-simulator tests + apiCheck all green;
Compose module compiles for JVM, Wasm and iOS.

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNode.kt

@@ -64,12 +64,19 @@ public open class TreeNode<T>(public val value: T, public val treeIterator: Tree
         if (child._parent != null) {
             throw TreeNodeException("$child already has a parent; call detach() before re-attaching it.")
         }
-        var ancestor: TreeNode<T>? = this
-        while (ancestor != null) {
-            if (ancestor === child) {
-                throw TreeNodeException("Adding $child here would create a cycle.")
+        if (child === this) {
+            throw TreeNodeException("Adding $child here would create a cycle.")
+        }
+        // Only a node that already has its own subtree can contain `this` and thus form a cycle.
+        // Skipping this walk for leaves keeps building deep trees O(n) instead of O(n²).
+        if (child._children.isNotEmpty()) {
+            var ancestor: TreeNode<T>? = _parent
+            while (ancestor != null) {
+                if (ancestor === child) {
+                    throw TreeNodeException("Adding $child here would create a cycle.")
+                }
+                ancestor = ancestor._parent
             }
-            ancestor = ancestor._parent
         }
         child._parent = this
         _children.add(child)