add batch client + test

[thehesiod]

No description provided.

[dazza-codes]

Apache 2.0 code related to this is available in

• https://gitlab.com/dazza-codes/python-notes/-/tree/master/notes/aio_aws
• https://gitlab.com/dazza-codes/python-notes/-/tree/master/tests/aio_aws

But IMO that code is a higher-order concern than aiobotocore. Also, that code may be split out of that project into its own project where additional features may be added, including small UI/app features.

[thehesiod]

hijacking this PR for some more cleanup as well :)

[codecov]

Codecov Report

Merging #773 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #773   +/-   ##
=======================================
  Coverage   88.74%   88.74%           
=======================================
  Files          16       16           
  Lines        1324     1324           
=======================================
  Hits         1175     1175           
  Misses        149      149           

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[thehesiod]

thanks @dazza-codes !