Centralize arithmetic tests for datetime/timedelta series

[jbrockmendel]

No tests were harming in the making of this PR.

[pep8speaks]

Hello @jbrockmendel! Thanks for submitting the PR.

• In the file pandas/tests/series/test_operators.py, following are the PEP8 issues :

Line 561:17: E741 ambiguous variable name 'l'
Line 564:17: E741 ambiguous variable name 'l'
Line 1390:13: E722 do not use bare except'

[codecov]

Codecov Report

Merging #18809 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18809      +/-   ##
==========================================
- Coverage   91.64%   91.62%   -0.02%     
==========================================
  Files         154      154              
  Lines       51430    51430              
==========================================
- Hits        47131    47122       -9     
- Misses       4299     4308       +9

Flag	Coverage Δ
#multiple	89.49% <ø> (ø)	⬆️
#single	40.83% <ø> (-0.12%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.68% <0%> (-0.11%)	⬇️

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[jreback]

thanks. so then you want another pass to parameterize some of these?

[jbrockmendel]

so then you want another pass to parameterize some of these?

Yah, plus break up by op. Ultimately I want to make sure same set of cases get tested for the datetimelike series as for the datetimelike indexes.