Reduce Unit Test Times (Part 3) (#3850)
* add coverage report
* define env vars in shared action
* reduce time for longest running tests
* fix broken shared action
* reduce test time
* reducing Pipeline test times
* further reducing test times
* rework Z3 test
* testing new mp.pool and persistent dist envs
* fix import
* reuse distributed environment for tests with lots of param combos
* fix for dist teardown
* fix pickling issue with pool cache
* actually fix pickling problem
* avoid running pool cache stuff on non-distributed tests
* fix issues with nested mp.pool
* fix for nested pools in Pipeline Engine
* re-add params
* update workflows with pytest opts
* implement feedback
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Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
