[Test Infrastructure] Configure pytest and pytest-asyncio

[beauremus]

Issue 1: [Test Infrastructure] Configure pytest and pytest-asyncio in pyproject.toml

Status: Implemented on branch chore/configure-pytest. Configuration and installation checks pass; full-suite verification remains blocked by the pre-existing Issue 2 regression test. No Issue 2 code changes were made, and work stops here pending Issue 2 approval.

Summary

Move the test-runner configuration and async test dependency into the project metadata so local development and CI use the same declared setup.

Context

• pyproject.toml currently declares only build, wheel, and setuptools-related development tooling; it does not declare pytest or pytest-asyncio.
• The GitHub Actions workflow installs pytest and flake8 directly in .github/workflows/python-package.yml.
• tests/test_dpm_task_context.py imports pytest and exercises asyncio behavior, but is currently written around a manually managed event loop rather than pytest-asyncio fixtures/markers.
• The package supports Python >=3.9.21; CI should cover Python 3.9 through 3.13, including the AlmaLinux 9.6 baseline (3.9.21).

Scope

• Add the required test dependencies and pytest configuration in pyproject.toml.
• Decide and document the appropriate pytest-asyncio mode and async-test conventions for this repository.
• Align CI installation with the declared development/test dependencies where appropriate.
• Do not change production behavior as part of this issue.

Acceptance criteria

• A clean development environment can install the declared test tooling from the project configuration.
• pytest discovers and runs the repository test suite without requiring ad hoc test-runner installation beyond the documented development install.
• Async tests have an explicit, consistent configuration and do not depend on implicit event-loop behavior.
• CI continues to run the test suite across the supported Python versions, with dependency compatibility verified.
• The resulting configuration is documented sufficiently for contributors to run the same checks locally.

Verification

• Clean virtual environment: pip install -e ".[dev]" succeeded and installed pytest, pytest-asyncio, build, and wheel from the project metadata.
• Async configuration smoke test: passed with asyncio_mode = "auto".
• Pytest collection: passed (1 test collected).
• Full python -m pytest -q: blocked by the existing tests/test_dpm_task_context.py expectation; it fails because the test does not raise the Issue 2 RuntimeError under the current Python 3.13 runtime.
• Python 3.9 dependency resolution: passed using compatible pytest/pytest-asyncio releases.
• Python 3.8 was removed from the CI matrix because the project minimum is Python 3.9.21 and AlmaLinux is now on Python 3.9.
• Wheel build: passed after installing the declared build backend dependencies; only pre-existing setuptools license deprecation warnings were emitted.
• No production package dependency was added solely for test infrastructure.

Dependencies and risks

• This issue should be completed before relying on pytest-asyncio-specific tests for Issues 2 or 3.
• pytest-asyncio compatibility with the repository's Python-version matrix must be checked before selecting a version constraint.
• CI currently uses continue-on-error: true for pytest; whether that policy should change is an explicit follow-up decision, not an assumed part of this issue.

Review focus

• Whether the dependency belongs in the existing dev optional-dependency group or a newly named test group.
• Whether the chosen async mode and event-loop scope are explicit and compatible with the test suite.
• Whether local and CI installation paths remain consistent.

Out of scope

• Fixing the DPM.replies() timeout failure (Issue 2).
• Refactoring set_many() synchronization (Issue 3).