feat(vm_provision_mixin): pin explicit NIC MAC when given

nics[i]['mac'] is set via virtio=<mac>,bridge=... instead of the bare
virtio,bridge=... form, so a caller-supplied MAC actually takes effect
(needed for DHCP reservations created before the VM exists).

napalm_proxmox/vm_provision_mixin.py

@@ -313,8 +313,9 @@ class ProxmoxVMProvisionMixin:
                 if not bridge:
                     raise ValueError(f"NIC {i}: bridge is required")
 
-                # Build base config: model + bridge
-                net_config = f"virtio,bridge={bridge}"
+                # Build base config: model[=mac] + bridge
+                mac = nic.get("mac")
+                net_config = f"virtio={mac},bridge={bridge}" if mac else f"virtio,bridge={bridge}"
 
                 # Add VLAN configuration (access vs trunk)
                 if "trunk_vlan_tags" in nic and nic["trunk_vlan_tags"]: