Make meshing compliant with bempp-cl

[DanielWinklehner]

Need to look into the meshing for BEMPP. Would be best to make py_electrodes independent of BEMPP, but return a usable mesh for electrode assemblies.

File "...\py_electrodes.py", line 320, in get_bempp_mesh
_vertices = mesh.leaf_view.vertices
AttributeError: 'Grid' object has no attribute 'leaf_view'

[pweigel]

Meshio (https://github.com/nschloe/meshio) may be the solution to this. It looks like a lot of people are starting to use it.

[DanielWinklehner]

Yes, maybe. We have to already provide it anyway for bempp-cl, so might as well use it.

[DanielWinklehner]

Update on this issue: bempp-cl seems to be inconsistent internally as to which version of meshio to use. Their current environment.yaml lists version 3.2.12. However, the simple Laplace example with Dirichlet boundaries fails at creating the mesh. When I update to meshio 4.0.10 (current latest), it works. However, then, if I want to use gmsh to plot the GridFunction, it tries to export to a mesh version that meshio no longer supports ("gmsh2-ascii"). In meshio 4 the supported formats are "gmsh" and "gmsh22". I manually override file_format in my local bempp-cl installation and then it works. I will submit a bug report with bempp-cl. Until this has been resolved, I will leave the issue open.