feat(py): add Worker, which runs model code in a persistent sandboxed Python session

.github/workflows/py-check.yaml

@@ -13,6 +13,8 @@ permissions: read-all
 jobs:
   check:
     runs-on: ${{ matrix.os }}
+    # A deadlock in the worker tests fails the leg instead of hanging it.
+    timeout-minutes: 20
     strategy:
       fail-fast: false
       matrix:
@@ -75,6 +77,7 @@ jobs:
     # kernel runs natively while tagging the syscalls with the 32-bit ABI,
     # so the live tests check the 32-bit tables against the kernel itself.
     runs-on: ${{ matrix.os }}
+    timeout-minutes: 10
     strategy:
       fail-fast: false
       matrix:

pkg-py/pyproject.toml

@@ -55,6 +55,8 @@ build-backend = "hatchling.build"
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 asyncio_mode = "auto"
+# A test still running after this many seconds prints every thread's stack.
+faulthandler_timeout = 300
 
 [tool.ruff]
 src = ["src", "tests"]