fix(vm_provision_mixin): destroy_vm's delete call rejected by Proxmox (400)

Passed destroy_unreferenced_disks (underscore) as a kwarg to proxmoxer's
delete(), but Proxmox's actual DELETE /nodes/{node}/qemu/{vmid} parameter
is hyphenated (destroy-unreferenced-disks). proxmoxer forwards kwargs to
the request verbatim with no underscore-to-hyphen translation, so Proxmox
rejected every call with "property is not defined in schema" before ever
touching the VM — the VM stayed fully intact (config, disks) despite the
caller believing destroy had at least been attempted. Fixed by building
the params as a dict (bypassing the Python-identifier restriction) with
the correct hyphenated key.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_vm_provision_mixin.py

@@ -451,6 +451,11 @@ def test_destroy_vm_success():
         mixin.destroy_vm("101", remove_disk=True, timeout=60)
 
     assert mock_vm.delete.called
+    # Proxmox's API parameter is hyphenated; passing the underscore form
+    # (a Python-identifier-friendly typo) gets silently rejected by Proxmox
+    # with a 400 "property is not defined in schema" instead of deleting.
+    _, delete_kwargs = mock_vm.delete.call_args
+    assert delete_kwargs == {"purge": 1, "destroy-unreferenced-disks": 1}
 
 
 def test_destroy_vm_already_stopped():