feat: shutdown_host and begin_stop_vm through the API

shutdown_host() posts command=shutdown to the node itself; its guests
stop as on any shutdown. begin_stop_vm(name) asks a guest for its clean
shutdown and returns once Proxmox took it, without waiting for the
task: the caller reads get_vm_status until it stopped. Both raise
RuntimeError when Proxmox refuses; an unknown guest is a ValueError.

The contracts HostShutdownMixin and VmStopRequestMixin of
napalm-device-types (NAPALM/napalm-device-types#55); for netOrk's graph
workflows (NetOrk/netork#1636).

CHANGELOG.md

@@ -7,6 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- `shutdown_host()`: the node shuts itself down through the API
+  (`POST /nodes/{node}/status command=shutdown`), and `begin_stop_vm(name)`: a
+  guest's clean shutdown, returning once Proxmox took it instead of waiting for
+  the task — the contracts `HostShutdownMixin` and `VmStopRequestMixin` of
+  napalm-device-types (NetOrk/netork#1636).
+
 ## [0.8.0] - 2026-10-23
 
 The first release on PyPI. It collects everything since 0.1.0.