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.

gradle/libs.versions.toml

@@ -6,6 +6,7 @@ binaryCompatibilityValidator = "0.16.3"
 kover = "0.8.3"
 coroutines = "1.9.0"
 kotlinxSerialization = "1.7.3"
+composeMultiplatform = "1.7.3"
 
 [plugins]
 kotlinMultiplatform = { id = "org.jetbrains.kotlin.multiplatform", version.ref = "kotlin" }
@@ -14,6 +15,8 @@ dokka = { id = "org.jetbrains.dokka", version.ref = "dokka" }
 mavenPublish = { id = "com.vanniktech.maven.publish", version.ref = "mavenPublish" }
 binaryCompatibilityValidator = { id = "org.jetbrains.kotlinx.binary-compatibility-validator", version.ref = "binaryCompatibilityValidator" }
 kover = { id = "org.jetbrains.kotlinx.kover", version.ref = "kover" }
+composeMultiplatform = { id = "org.jetbrains.compose", version.ref = "composeMultiplatform" }
+composeCompiler = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
 
 [libraries]
 kotlinx-coroutines-core = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "coroutines" }