feat: VM snapshots and reboot_host through the API

get_vm_snapshots, create_vm_snapshot, delete_vm_snapshot and
rollback_vm_snapshot for VMs and containers, so netOrk's snapshot view
works on Proxmox as it does on VMware. Proxmox lists the live state as a
pseudo-snapshot named "current"; it is never reported or addressable.
Containers have no RAM state, so include_memory is ignored for them.

reboot_host() restarts the node with POST /nodes/{node}/status
command=reboot instead of /sbin/reboot over SSH.

tests/test_reboot_host.py

@@ -0,0 +1,16 @@
+"""reboot_host: restart the Proxmox node itself through the API, not over SSH."""
+
+from __future__ import annotations
+
+import pytest
+
+
+def test_posts_reboot_to_the_node(driver):
+    driver.reboot_host()
+    driver._node_api().status.post.assert_called_once_with(command="reboot")
+
+
+def test_api_refusal_is_a_runtime_error(driver):
+    driver._node_api().status.post.side_effect = Exception("Permission check failed")
+    with pytest.raises(RuntimeError, match="Permission check failed"):
+        driver.reboot_host()