chore: add test + lint tooling (pyproject, Makefile)

Poetry/pytest/ruff/black/mypy config mirroring the aio extension lint
pipeline (spirekeeper template). `make test` runs pytest; `make check`
runs the linters. Enables a tests/ suite for the extension.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VUQCfdqiLSsFS2jcGnaFD

Makefile

@@ -0,0 +1,25 @@
+all: format check
+
+format: black ruff
+
+check: mypy checkblack checkruff
+
+mypy:
+	poetry run mypy .
+
+black:
+	poetry run black .
+
+ruff:
+	poetry run ruff check . --fix
+
+checkruff:
+	poetry run ruff check .
+
+checkblack:
+	poetry run black --check .
+
+test:
+	PYTHONUNBUFFERED=1 \
+	DEBUG=true \
+	poetry run pytest