[mypy] fix type annotations for graphs/a_star.py #4052 (#5224)

* [mypy] fix type annotations for graphs/a_star.py #4052

* updating DIRECTORY.md

* Add from __future__ import anotations

* rename delta by DIRECTIONS

Co-authored-by: John Law <[email protected]>

* Rename delta by DIRECTIONS in all code

* Enclose script in __main__ code block

* Refactor DIRECTIONS with comments for readibility

* Delete heuristic example comment

* Do not print, return all values

* Fix multilines

* fix black

* Update a_star.py

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: John Law <[email protected]>