fix: handling non-string values for column headers

[pjaselin]

Close #178

This handles where column titles may not be strings (e.g. floats)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.26%. Comparing base (87cd1b0) to head (84b87dd).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
- Coverage   98.26%   98.26%   -0.01%     
==========================================
  Files          12       12              
  Lines         520      519       -1     
  Branches       80       80              
==========================================
- Hits          511      510       -1     
  Misses          6        6              
  Partials        3        3              

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