feat: add blockbuster & fix docker

tests/conftest.py

@@ -0,0 +1,25 @@
+from typing import Iterator
+
+import pytest
+from blockbuster import BlockBuster, blockbuster_ctx
+
+
+@pytest.fixture(autouse=True)
+def _no_blocking_in_async(
+    request: pytest.FixtureRequest,
+) -> Iterator[BlockBuster | None]:
+    """Guard all async tests against accidental blocking I/O calls.
+
+    Uses blockbuster to raise ``BlockingError`` whenever a known blocking
+    function (e.g. ``open``, ``time.sleep``, socket I/O) is invoked inside
+    an asyncio event loop, which would stall the loop and hide bugs.
+
+    The guard is skipped for synchronous tests so as not to affect them.
+    """
+    if request.node.get_closest_marker("asyncio") is None:
+        # Not an async test — nothing to guard.
+        yield
+        return
+
+    with blockbuster_ctx():
+        yield