Refactor: Externalize .LevelReduction and .GetKingdom for global use

[teddyCodex]

Description

Defines .LevelReduction and .GetKingdom outside of the plotLineageHeatmap function, eliminating the need for functions within a function and making them globally accessible.

devtools::check() - 0 errors

Fixes issue #80

What kind of change(s) are included?

• [ ] Feature (adds or updates new capabilities)
• [ ] Bug fix (fixes an issue).
• [x] Enhancement (code refactor).
• [ ] Breaking change (these changes would cause existing functionality to not work as expected).

Checklist

Please ensure that all boxes are checked before indicating that this pull request is ready for review.

• [x] I have read and followed the CONTRIBUTING.md guidelines.
• [x] I have searched for existing content to ensure this is not a duplicate.
• [x] I have performed a self-review of these additions (including spelling, grammar, and related).
• [x] I have added comments to my code to help provide understanding.
• [x] I have added a test which covers the code changes found within this PR.
• [x] I have deleted all non-relevant text in this pull request template.
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[the-mayer]

Thanks @teddyCodex, just added a quick comment to verify that we aren't breaking the plot code. Note, I've also invited @Joiejoie1 to provide a review as they have also been working on this issue. Thanks both!

[Joiejoie1]

Thanks @teddyCodex, just added a quick comment to verify that we aren't breaking the plot code. Note, I've also invited @Joiejoie1 to provide a review as they have also been working on this issue. Thanks both!

Thamks @the-mayer I'll do just that

[jananiravi]

Good work, @teddyCodex @Joiejoie1! thanks for the PR!