TST: Use new arithmetic fixtures, parametrize many more tests

[jbrockmendel]

Focus is mostly on test_datetime64.py to keep things close to orthogonal.

De-duplicates some tests that are in e.g. both TestFrameArithmetic and TestSeriesArithmetic

[pep8speaks]

Hello @jbrockmendel! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/tests/arithmetic/conftest.py !

• There are no PEP8 issues in the file pandas/tests/arithmetic/test_datetime64.py !

• There are no PEP8 issues in the file pandas/tests/arithmetic/test_numeric.py !

• There are no PEP8 issues in the file pandas/tests/arithmetic/test_period.py !

• There are no PEP8 issues in the file pandas/tests/arithmetic/test_timedelta64.py !

• There are no PEP8 issues in the file pandas/tests/indexes/test_numeric.py !

[jreback]

looks fine. lots of tests :-D

[jbrockmendel]

looks fine. lots of tests :-D

Yep, and you better believe we're not done yet. Working on a test_timedelta64 branch for after #23642.

[codecov]

Codecov Report

Merging #23757 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #23757      +/-   ##
==========================================
+ Coverage   92.23%   92.24%   +0.01%     
==========================================
  Files         161      161              
  Lines       51408    51408              
==========================================
+ Hits        47416    47422       +6     
+ Misses       3992     3986       -6

Flag	Coverage Δ
#multiple	90.63% <ø> (+0.01%)	⬆️
#single	42.3% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/util/testing.py	85.56% <0%> (+0.56%)	⬆️

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[jreback]

thanks @jbrockmendel