ci: centralize pytest configuration in root

[SilanHe]

Issue #, if available:

Description of changes: We are getting new warnings for unknown pytest mark when running integration tests.

There are some warnings in the newest integration test CI workflow
packages/aws-durable-execution-sdk-python-examples/test/step/test_step.py:10
/home/runner/work/aws-durable-execution-sdk-python/aws-durable-execution-sdk-python/language-sdk/packages/aws-durable-execution-sdk-python-examples/test/step/test_step.py:10: PytestUnknownMarkWarning: Unknown pytest.mark.example - is this a typo? You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/how-to/mark.html
@pytest.mark.example Is this something caused by the mono repo change? There was no warning before (e.g. test run history) - @wangyb-A

For this PR, I'm moving duplicated [tool.pytest.ini_options] sections from sub-package pyproject.toml files to the root pyproject.toml. All pytest runs happen from the repo root, so markers, testpaths, and addopts only need to live in the root config.

Issue accidentally introduced in https://github.com/aws/aws-durable-execution-sdk-python/pull/397/changes#r3327105014

Testing: I ran the hatch run test:cov from the project root and there are no more warnings.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[zhongkechen]

curious why we need --import-mode=importlib

[SilanHe]

it's because of the new monorepo, if we have tests in 2 packages with the same file name, they will normally collide since the --import-mode is by default prepend. importlib mode uses Python's importlib to import each test file as a unique module based on its full file path, so there's no collision.

https://docs.pytest.org/en/7.1.x/explanation/pythonpath.html