feat: shutdown_host and begin_stop_vm, shutting down without waiting

HostShutdownMixin.shutdown_host(), on DeviceTypeDriver: a device shuts
itself down cleanly through its own means; declared, so hasattr says
whether a driver can. There is no forced variant.

VmStopRequestMixin.begin_stop_vm(name): ask for a VM's clean shutdown
and return at once, for a caller that waits on a timer and reads
get_vm_status instead of blocking in stop_vm. No role demands it.

For netOrk's graph workflows, which switch a hypervisor off when CI has
nothing for it (NetOrk/netork#1636).

tests/test_host_shutdown.py

@@ -0,0 +1,27 @@
+"""shutdown_host: the contract for shutting the device itself down cleanly.
+
+netOrk's graph workflows switch a hypervisor off when it has nothing to do
+(NetOrk/netork#1636): through its own API, never by pulling the power. Like
+``reboot_host`` it is declared, not implemented, so ``hasattr`` tells netOrk
+whether a driver can.
+"""
+
+from __future__ import annotations
+
+import inspect
+
+from napalm_device_types import DeviceTypeDriver, HostShutdownMixin
+
+
+def test_every_device_type_driver_carries_the_declaration():
+    assert issubclass(DeviceTypeDriver, HostShutdownMixin)
+
+
+def test_declared_not_implemented():
+    assert not hasattr(DeviceTypeDriver, "shutdown_host")
+
+
+def test_declaration_documents_the_contract():
+    source = inspect.getsource(HostShutdownMixin)
+    assert "def shutdown_host(self) -> None" in source
+    assert "RuntimeError" in source

tests/test_vm_stop_request.py

@@ -0,0 +1,28 @@
+"""begin_stop_vm: ask for a VM's clean shutdown and return at once.
+
+``stop_vm`` blocks until the VM is stopped, with a limit of the driver's own.
+A caller that keeps its waits as timers (netOrk's graph workflows,
+NetOrk/netork#1636) asks with ``begin_stop_vm`` and reads ``get_vm_status``
+until the VM is stopped. A driver mixes it in when it can; no role demands it.
+"""
+
+from __future__ import annotations
+
+import inspect
+
+from napalm_device_types import HypervisorDriver, VmStopRequestMixin
+
+
+def test_no_role_demands_it():
+    assert not issubclass(HypervisorDriver, VmStopRequestMixin)
+
+
+def test_declared_not_implemented():
+    assert not hasattr(VmStopRequestMixin, "begin_stop_vm")
+
+
+def test_declaration_documents_the_contract():
+    source = inspect.getsource(VmStopRequestMixin)
+    assert "def begin_stop_vm(self, name: str) -> None" in source
+    assert "ValueError" in source
+    assert "RuntimeError" in source