message: ek.set_label(var_1=var_1, var_2=var_2, ..) syntax
diff: @@ -1370,7 +1370,13 @@ def label(a):
  return None
  -def set_label(a, label):
  +def set_label(*args, **kwargs):
  + n_args, n_kwargs = len(args), len(kwargs)
  + if (n_kwargs and n_args) or (n_args and n_args != 2):
  + raise Exception('set_label(): invalid input arguments')
  +
  + if n_args:
  + a, label = args
  if _ek.is_jit_array_v(a) or _ek.is_diff_array_v(a):
  a.set_label_(label)
  elif isinstance(a, _Mapping):
  @@ -1379,6 +1385,9 @@ def set_label(a, label):
  elif _ek.is_enoki_struct_v(a):
  for k in a.ENOKI_STRUCT.keys():
  set_label(getattr(a, k), label + "_" + k)
  + elif n_kwargs:
  + for k, v in kwargs.items():
  + set_label(v, k)
  def schedule(*args):
  