Cleanup test classes to eliminate warnings coming from PyTest.

[cleemullins]

Fixes #167

Resolved all Pytest warnings. Mostly by renaming and/or rescoping test supporting classes that were incorrectly being picked up as tests. For some classes, this was a rename. Detailed info on each issue resolves is found in #167.

Added in a pytest.ini file to automatically run all the tests in strict / warnings-as-error mode. This should cause the local builds, GitHub builds, and ADO builds to all run tests in the same way.

The only code error fixed was in the CosmosDB storage provider which was failing to close the config file after loading it to JSON. This was flagged by PyTest as a resource leak once the strict mode was enabled, so I cleaned that up.

[Copilot]

Pull Request Overview

This PR eliminates pytest warnings by renaming test support classes that were incorrectly being detected as test classes by pytest's automatic discovery. The changes rename various test helper classes to use either a leading underscore or "Mock" prefix to indicate they are supporting utilities rather than test classes.

• Renamed test support classes to avoid pytest auto-discovery (using _ prefix or Mock prefix)
• Updated all references to the renamed classes throughout the test files
• Cleaned up an obsolete test client class name for clarity

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/hosting_core/test_turn_context.py	Renamed TestingSimpleAdapter to _SimpleTestingAdapter and updated all references
tests/hosting_core/storage/test_transcript_logger_middleware.py	Updated imports and references from TestingAdapter to MockTestingAdapter
tests/hosting_core/state/test_agent_state.py	Renamed TestDataItem to _MockTestDataItem and updated all references from TestingAdapter/TestingCustomState to their Mock prefixed versions
tests/_integration/common/testing_environment.py	Updated reference from TestingAdapter to MockTestingAdapter
tests/_common/testing_objects/mock_testing_custom_state.py	Renamed class from TestingCustomState to MockTestingCustomState
tests/_common/testing_objects/adapters/mock_testing_adapter.py	Renamed class from TestingAdapter to MockTestingAdapter
tests/_common/testing_objects/adapters/init.py	Updated exports to reflect the renamed adapter class
tests/_common/testing_objects/init.py	Updated imports and exports for the renamed mock classes
tests/_common/obsolete_test_client.py	Renamed TestClient to ObsoleteTestClient to clarify its obsolete status

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