[ENH] improve performance for polars' complete

[samukweku]

PR Description

Please describe the changes proposed in the pull request:

• remove ambiguity for multiple columns - user creates a struct before calling complete
• update code to remove performance warning ( uses collect_schema instead of columns)

This PR relates to #1352 .

PR Checklist

Please ensure that you have done the following:

1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

2. If you're not on the contributors list, add yourself to AUTHORS.md.

3. Add a line to CHANGELOG.md under the latest version header (i.e. the one that is "on deck") describing the contribution.
   • Do use some discretion here; if there are multiple PRs that are related, keep them in a single line.

Automatic checks

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• Building a preview of the docs on Netlify
• Automatically linting the code
• Making sure the code is documented
• Making sure that all tests are passed
• Making sure that code coverage doesn't go down.

Relevant Reviewers

Please tag maintainers to review.

• @ericmjl

[ericmjl]

🚀 Deployed on https://deploy-preview-1389--pyjanitor.netlify.app

[codecov]

Codecov Report

Attention: Patch coverage is 96.96970% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.39%. Comparing base (62c57c6) to head (911abd8).
Report is 33 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1389      +/-   ##
==========================================
- Coverage   94.48%   88.39%   -6.09%     
==========================================
  Files          80       87       +7     
  Lines        4367     5352     +985     
==========================================
+ Hits         4126     4731     +605     
- Misses        241      621     +380     

[ericmjl]

Looking great, @samukweku! Please do the honors of hitting the merge button!