ref(sessions): Split up sessions tests into more TestCase classes

[ryan953]

The problem is that many of these tests share the same set of session data to assert against and in a followup I'm going to split many of these tests into two parts, one to test crashed state (as we do now) and another set that will run through the unhandled state.

So what this PR does is run through all the tests and co-location the self.store_sessions() or self.bulk_store_sessions() calls into the test that needs it. Some tests don't even need those mocks and speedup just a little tiny bit.
As i was going through i tried to isolate things that were not re-used across tests or testcases, and improve names when i could.

Now what we have is a base class ReleaseHealthBaseTestCase which is a place to hold collections of re-usable session mocks. Right now there are two scenarios in there with some number of crashes. Soon to be more!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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##           master   #97048       +/-   ##
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+ Coverage   69.06%   80.68%   +11.61%     
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  Files        8516     8523        +7     
  Lines      374209   374554      +345     
  Branches    24334    24334               
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+ Hits       258442   302193    +43751     
+ Misses     115391    71985    -43406     
  Partials      376      376