Mesh3D plot: positions do not update

[nvaytet]

Example:

import scipp as sc
import plopp as pp
from plopp.data import examples

dg = sc.io.load_hdf5(examples.teapot())

v = pp.Node(dg["vertices"])
f = pp.Node(dg["faces"])
c = pp.Node(dg["vertices"].fields.z)

fig = pp.mesh3d(
    vertices=v,
    faces=f,
    vertexcolors=c,
)
fig

and then

v.func = lambda: dg["vertices"] * 2.0
v.notify_children("")

has no effect.

See TODO in the code.