Refactor for readability and avoid merge conflicts

[hugovk]

Will help avoid and simplify resolution of merge conflicts like from #104 and #114.

Also more readable. (And save some function calls.)

[codecov]

Codecov Report

Merging #119 (fad55c7) into master (ff2501d) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #119      +/-   ##
==========================================
- Coverage   91.09%   91.07%   -0.03%     
==========================================
  Files           3        3              
  Lines        1707     1703       -4     
==========================================
- Hits         1555     1551       -4     
  Misses        152      152              

Flag	Coverage Δ
GHA_Ubuntu	91.07% <100.00%> (-0.03%)	⬇️
GHA_Windows	91.07% <100.00%> (-0.03%)	⬇️
GHA_macOS	91.07% <100.00%> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
src/prettytable/prettytable.py	87.29% <100.00%> (-0.05%)	⬇️
tests/test_prettytable.py	100.00% <100.00%> (ø)

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