Use readonly tree in bstm

Author: Eric-Warehime

blockstm/btree.go

@@ -14,8 +14,9 @@ type BTree[T any] struct {
 // NewBTree returns a new BTree.
 func NewBTree[T any](less func(a, b T) bool, degree int) *BTree[T] {
 	tree := btree.NewBTreeGOptions(less, btree.Options{
-		NoLocks: true,
-		Degree:  degree,
+		NoLocks:  true,
+		ReadOnly: true,
+		Degree:   degree,
 	})
 	t := &BTree[T]{}
 	t.Store(tree)