Additional validation checks for `columnIndexFromString()` and `stringFromColumnIndex()` methods

[MarkBaker]

This is:

- [X] a bugfix
- [ ] a new feature
- [ ] refactoring
- [ ] additional unit tests

Checklist:

• [X] Changes are covered by unit tests
  • [X] Changes are covered by existing unit tests
  • [X] New unit tests have been added
• [X] Code style is respected
• [X] Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• [ ] CHANGELOG.md contains a short summary of the change
• [ ] Documentation is updated as necessary

Why this change is needed?

Additional validation, because it is clear that some people are passing numeric values to columnIndexFromString()