Allow s3 testing in face of ambient AWS credentials

[chuckwondo]

This PR allows tests that use s3fs to run successfully in environments where there are "ambient" AWS credentials (i.e., either AWS_* env vars set or presence of ~/.aws/config) and the AWS region is set to something other than "us-east-1". In such cases, tests using s3fs fail with IllegalLocationConstraintException.

This PR allows tests to succeed in such environments (i.e., typically a local dev setup). Further, since mypy was failing during pre-commit for code in the module tests.test_store.test_fsspec, it also adds that module to the mypy "ignore" list in pyproject.toml until mypy configuration can be addressed to avoid the problem (to be addressed in a separate PR that will make mypy execution more robust/consistent). In the process of diagnosing the mypy error, I updated the mypy configuration to provide more informative output.

Finally, I adjusted a test fixture to eliminate the "noise" of the "AssertionError: Session was never entered" message (and traceback) upon completion of test execution, which is disconcerting and confusing (made me wonder how the tests all passed while showing a traceback).

TODO:

• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.23%. Comparing base (85890b3) to head (54970a8).
⚠️ Report is 142 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3947   +/-   ##
=======================================
  Coverage   93.23%   93.23%           
=======================================
  Files          87       87           
  Lines       11695    11695           
=======================================
  Hits        10904    10904           
  Misses        791      791           

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[d-v-b]

thanks for this @chuckwondo!