feat: implement the HypervisorDriver VM contract

start_vm, stop_vm, reboot_vm, suspend_vm and get_vm_config existed only
as declarations. netOrk called Proxmox's own power_vm and read a VM's
raw config through _node_api(), so no other hypervisor could serve the
same endpoints. These let netOrk talk to every hypervisor alike.

The power methods accept a VM's name or vmid, wait for the Proxmox task,
and raise ValueError/RuntimeError as the contract says instead of
returning a result dict. A forced reboot of a container is stop + start,
since LXC has no reset; suspending a container is refused. power_vm is
unchanged for existing callers.

get_vm_config moves the config parsing netOrk did in
_parse_proxmox_hw_config into the driver and returns a VMConfigDict:
disks with storage and size, NICs with model, MAC, bridge and VLAN, CPU
topology, firmware, machine type and PCI/USB passthrough.

get_vms reports vmid as a string ("100"), following
napalm-device-types 2.0, still ordered numerically.

napalm_proxmox/driver.py

@@ -49,6 +49,7 @@ from napalm_proxmox.sdn_mixin import ProxmoxSDNMixin
 from napalm_proxmox.lldp_mixin import ProxmoxLLDPMixin
 from napalm_proxmox.config_mixin import ProxmoxConfigMixin
 from napalm_proxmox.vm_mixin import ProxmoxVMMixin
+from napalm_proxmox.vm_contract_mixin import ProxmoxVMContractMixin
 from napalm_proxmox.vm_provision_mixin import ProxmoxVMProvisionMixin
 from napalm_proxmox.routing_mixin import ProxmoxRoutingMixin
 from napalm_proxmox.system_mixin import ProxmoxSystemMixin
@@ -69,6 +70,7 @@ class ProxmoxDriver(
     ProxmoxLLDPMixin,
     ProxmoxConfigMixin,
     ProxmoxVMMixin,
+    ProxmoxVMContractMixin,
     ProxmoxVMProvisionMixin,
     ProxmoxRoutingMixin,
     ProxmoxSystemMixin,