Enhance find_outliers and identify_outliers performance by avoiding duplication and filtering columns

[d33bs]

Description

This PR enhances find_outliers and identify_outliers performance by filtering to only the necessary columns and avoiding data duplication where possible. Along the path towards this PR I also analyzed code coverage and found we needed to clean up a bunch of legacy fixtures which are no longer used here (should boost the coverage percentage overall now as a result).

Closes #134
Closes #86

What kind of change(s) are included?

• Documentation (changes docs or other related content)
• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• 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.

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

[jenna-tomkinson]

LGTM! 🎉 Love this small change! Just curious, is this behavior going to be the default and the user can choose to load in all columns?

[d33bs]

Thanks @jenna-tomkinson, merging this in!