Fix some pylint findings

[hugovk]

Fix some pylint findings:

• Don't shadow ordinal function
• More descriptive variable name: u -> unit
• Remove unnecessary elif and else after return: less certain about some of these, but I think it reduces complexity of some quite deeply nested code

Fix tests:

• Add missing assert to test
• Remove redundant comparison

[codecov-commenter]

Codecov Report

Merging #42 (d2bd73e) into main (5dc4b82) will increase coverage by 0.14%.
The diff coverage is 97.82%.

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
+ Coverage   99.12%   99.27%   +0.14%     
==========================================
  Files           9        9              
  Lines         686      686              
==========================================
+ Hits          680      681       +1     
+ Misses          6        5       -1     

Flag	Coverage Δ
macos-latest	97.52% <97.82%> (+0.14%)	⬆️
ubuntu-latest	97.52% <97.82%> (+0.14%)	⬆️
windows-latest	97.23% <97.82%> (+0.14%)	⬆️

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Impacted Files	Coverage Δ
src/humanize/number.py	96.89% <93.75%> (ø)
src/humanize/filesize.py	100.00% <100.00%> (ø)
src/humanize/time.py	100.00% <100.00%> (+0.46%)	⬆️
tests/test_i18n.py	100.00% <100.00%> (ø)
tests/test_time.py	100.00% <100.00%> (ø)

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