New shape to load 3D objects

[JonathanMaes]

This PR adds a new Shape, which can load a 3D object from STL, PLY, OBJ or GLTF/GLB files.
This ObjShape takes quite a few arguments:

• The name of the file to be loaded
• Exactly 2 of the following parameters to define the object's bounding box: min_point, max_point, center, scale and size. The last two of these parameters are mutually exclusive.
• Optional:
  • keep_aspect (default False): expand to the bounding box defined by the previous parameters without distortion.
  • repair (default False): try to make the shape watertight if it is not. A simply-connected object is assumed.
  • rotate_z_up (default True): most 3D objects use the y-axis as the vertical direction, while in mumax this is the z-axis.

Example: magnetization of a teapot

from mumaxplus import Ferromagnet, World, Grid
from mumaxplus.util import show_field_3D, ObjShape

N, L = 64, 512e-9
shape = ObjShape("teapot.obj", (0, 0, 0), size=(L, L, L), keep_aspect=True, rotate_z_up=True)
world = World(cellsize=(L/N, L/N, L/N))
magnet = Ferromagnet(world, Grid((N, N, N)), geometry=shape)
magnet.msat = 800e3
magnet.aex = 13e-12
magnet.relax()
show_field_3D(magnet.magnetization, enable_quiver=False)

Other changes

• Renamed the 'show' optional dependency group to '3D' and added trimesh and networkx to it. These optional dependencies should therefore now be installable alongside mumax⁺ with pip install mumaxplus[3D]
• Initializing a geometry now uses the shape_func directly if it is already vectorized, otherwise it falls back to _np.vectorize like before
• Added this shape to examples/shape.ipynb, where the quintessential teapot is loaded
• Fixed formatting in Torus and repeat documentation

[DiegoDeGusem]

Nice!