feat: Binary tree node sum (#7020) (#7162)

* feat: Binary tree node sum (#7020)

* feat: Sum of all nodes in binary tree explanation (#7020)

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update data_structures/binary_tree/binary_tree_node_sum.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* refactor: Change replace method with `__iter__` overriding (#7020)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>