Use cell_autofit_width to calculate column widths

[ldavies99]

Proposed Changes

Related Issues

• Fixes An alternative approach for auto column widths #155
• Fixes auto_width sets 0 widths for non-string type column headers #125

Pre-requisites

This section may not be fully required if the branch is not merging into main.
Please indicate items that aren't necessary and why, with comments around incomplete checks.

• Version number has been incremented, according to SemVer
• Changelog has been updated, listing changes to this version. Use the keep a changelog format
• New features are tested
• New features are documented using the numpydoc docstring format
• Other relevant package documentation is updated
• For new functionality, examples are included in the docs or a feature request has
  been made for it/them.

[ldavies99]

If you run pytest on the branch, you can compare the actual_workbook.xlsx and expected_workbook.xlsx under gptables/test/ to see the affects of the changes.

[addledrabbit]

Will pick this review up when I’m back from A/L on Wednesday.

[Sara-Jade-O]

Updated logic looks good to me - happy to merge