avoid re-validation for excluded features

[johnarevalo]

If an operation excluded a column, such column should not be validated by further operations. This will reduce the computation time. It will benefit list of operations sorted by computational cost (ascending).

What is the nature of your change?

• Enhancement (speed).
• This change requires a documentation update. Maybe explain the benefits of sorting operations by computational cost.

Checklist

• I have read the CONTRIBUTING.md guidelines.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• New and existing unit tests pass locally with my changes.
• I have deleted all non-relevant text in this pull request template.

[gwaybio]

@johnarevalo - is this ready for me to take a look? If so, please tag me

[johnarevalo]

Thanks for your reply @gwaybio, yes this is ready for your input.

[gwaybio]

I am excited about this change!

One comment worth discussion in the test but then I think this is straightforward to merge