Add test infrastructure: pytest, pytest-asyncio, respx

[heikkih]

Summary

This PR establishes a proper test suite for pyprusalink, replacing the current lint-only CI with real unit tests. It is the first in a planned series of improvements to both this library and the Home Assistant prusalink integration.

What's included

• requirements-test.txt: adds pytest, pytest-asyncio, and respx
• pyproject.toml: adds [tool.pytest.ini_options] with asyncio_mode = "auto" and corrects the Python classifier versions (3.9/3.10 → 3.11/3.12 to match CI)
• .github/workflows/test.yml: extends linting to the tests/ directory and adds a pytest tests/ step
• tests/conftest.py: shared fixtures
• tests/test_client.py: covers ApiClient error handling (InvalidAuth on 401, Conflict on 409, NotFound on 404) and DigestAuthWorkaround behaviour (omits algorithm without qop, delegates to parent when qop is present)
• tests/test_prusalink.py: happy-path coverage for all existing PrusaLink public methods (get_version, get_info, get_status, get_job, get_legacy_printer, cancel_job, pause_job, resume_job, get_file), including the 204 no-job case

All 15 tests pass in ~0.1s.

Planned follow-up PRs

Once this lands, the next PRs in the series will:

1. Remove DigestAuthWorkaround — both upstream issues are now resolved (httpx 0.27.0, Feb 2024; Prusa firmware 5.2.0, Feb 2024). The workaround can be dropped once firmware 5.2.0+ is the minimum supported version.
2. Add continue_job() — the missing complement to pause_job/resume_job for timelapse workflows.
3. Type the meta field in JobFilePrint with a proper PrintFileMetadata TypedDict, exposing filament type, material name, estimated usage, layer height, etc.
4. Expose transfer, storage, and camera sub-objects already returned by GET /api/v1/status but currently ignored.
5. New endpoints: get_storage(), get_transfer(), get_camera_snapshot(), get_update_info().

The goal is to give the Home Assistant integration richer, well-typed data to work with — enabling sensors for filament type, storage free space, upload progress, live camera snapshots, and firmware update availability.

Test plan

• pytest tests/ -v — 15 passed
• flake8 pyprusalink tests — no errors
• black --check pyprusalink tests — no reformats needed
• isort --check pyprusalink tests — no changes needed

🤖 Generated with Claude Code

[heikkih]

Quick note:

• I've got more PR's in the pipeline, but waiting on initial feedback before I'll proceed :)

[agners]

Thank you for working on this!