Refactor: Make use of constants class

[kayjan]

Description

Testing

Additional notes

Checklist

I have read through the contributing guidelines and ensured that

• I have added a descriptive title for this pull request.
• I have followed the convention and standards, and my code is checked for style and correctness.
• I have added test cases, and unit tests pass with 100% code coverage.
• I have updated the documentation and code docstrings.

Checklist (for reviewer)

• I have added label (breaking / enhancement / bug / documentation) to this pull request, if applicable.
• I will ensure this change is captured in the CHANGELOG.md file.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
bigtree	100%	100%	0	✔
bigtree.binarytree	100%	100%	0	✔
bigtree.dag	100%	100%	0	✔
bigtree.node	100%	100%	0	✔
bigtree.tree	100%	100%	0	✔
bigtree.tree.construct	100%	100%	0	✔
bigtree.tree.export	100%	100%	0	✔
bigtree.utils	100%	100%	0	✔
Summary	100% (2568 / 2568)	100% (1046 / 1046)	0	✔