BREAKING changes to the core:
- treeIterator is now a read-only `val`; added `iterator(order)` and use `asSequence(order)`.
- removeChild() only removes a direct child of the receiver; added `detach()` to unhook a node.
- addChild() rejects re-parenting and cycles (throws TreeNodeException); detach() first to move.
- clear() no longer nulls the receiver's own parent; only removes descendants.
- path() returns List<TreeNode<T>>? (null) instead of throwing.
Also:
- Enable strict explicitApi() across core + both modules; add explicit `public` modifiers.
- Update tests for the new contracts + add TreeNodeV4Test; refresh .api baselines.
- README + CHANGELOG (with migration notes); bump version to 4.0.0.
47 JVM tests green.
- Remove stray println(child.value) from TreeNode.removeChild()
- Add regression test for removeChild() return value
- Delete leftover ExampleUnitTest.kt template test
- Remove Example.ws.kts worksheet and kotlin("script-runtime") from jvmMain
- Bump actions/checkout v2 -> v4 in CI workflows
- Update README install snippets to 3.1.5
- Bump version to 3.1.5
