bugfix our center() padding algorithm

[jquast]

as written, we failed to look into the details of an oddity in
the padding of std python's center(),
https://jazcap53.github.io/pythons-eccentric-strcenter.html

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing jq/bugfix-center-parity-padding (d622de1) with master (a1b9a83)}

Summary

✅ 38 untouched benchmarks

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a1b9a83) to head (d622de1).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #188   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines          606       606           
  Branches       146       146           
=========================================
  Hits           606       606           

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