add iterators for tree

tree_iter.go

@@ -0,0 +1,33 @@
+package stl
+
+import "iter"
+
+func (t *Tree[K, V, C]) Keys() iter.Seq[K] {
+	return func(yield func(K) bool) {
+		for cur := t.FirstNode(); cur != nil; cur = cur.Next() {
+			if !yield(cur.key) {
+				return
+			}
+		}
+	}
+}
+
+func (t *Tree[K, V, C]) Values() iter.Seq[V] {
+	return func(yield func(V) bool) {
+		for cur := t.FirstNode(); cur != nil; cur = cur.Next() {
+			if !yield(cur.Value) {
+				return
+			}
+		}
+	}
+}
+
+func (t *Tree[K, V, C]) All() iter.Seq2[K, V] {
+	return func(yield func(K, V) bool) {
+		for cur := t.FirstNode(); cur != nil; cur = cur.Next() {
+			if !yield(cur.key, cur.Value) {
+				return
+			}
+		}
+	}
+}