Fix `mypy` errors in `dilation_operation.py` (#8595)

* updating DIRECTORY.md

* Fix mypy errors in dilation_operation.py

* Rename functions to use snake case

* updating DIRECTORY.md

* updating DIRECTORY.md

* Replace raw file string with pathlib Path

* Update digital_image_processing/morphological_operations/dilation_operation.py

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

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Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>