Update per-test config to be unique per-test in spec_configured_state_test

[ralexstokes]

Alternative fix for the issue addressed in #2755.

As I understand it, the issue there was that using the spec_configured_state_test decorator was not "thread-safe" so that any unsynchronized access could cause issues. These issues were seen in #2752 when executing the tests with pytest-xdist which parallelizes tests across multiple cores.

@hwwhww found the issue and suggested a fix w/ lazy loading of the modules in the pyspec.

Rather than go around making multiple copies of various modules, this PR takes a different approach to tests using the spec_configured_state_test decorator: simply make a separate copy of the Spec object.

As long as instances of Spec don't get too big or resource-intensive then we should be able to easily specialize a given Spec for each test that uses this decorator by simply making a copy and making the necessary edits.

As far as I can tell, there is no reason to "restore" the spec after mutation as it is discarded after the result from the decorated test is obtained.

[ralexstokes]

update: the Spec is a python module where we cannot simply just copy it. thinking of other solutions....

[ralexstokes]

after chatting w/ @hwwhww came to the current solution using importlib to load a fresh copy of the spec per test that needs to customize it, but skipping the lazy loading in #2755 and also only loading a duplicate in the specific tests that need customization, not every test

[ralexstokes]

there is some strange failure w/ a test (test_config_override) that seems to pass on dev

but ignoring that for now, i'd suggest we do something like this PR instead of #2755 to fix #2752 (and anything else that uses that decorator) as it provides a distinct, scoped instance of the spec to each test that wants to mutate it.

[hwwhww]

Big thanks to @ralexstokes ✨

Compared to #2755, it gets rid of the needless imports largely. Well done!