Add ignore_orientation and ignore_interior_facets flags

[kinnala]

In [1]: from skfem import *

In [2]: %time m = MeshTet.load('labelled.msh')

CPU times: user 632 ms, sys: 27.8 ms, total: 660 ms
Wall time: 704 ms

becomes

In [1]: from skfem import *

In [2]: %time m = MeshTet.load('labelled.msh', ignore_orientation=True)

CPU times: user 193 ms, sys: 31.8 ms, total: 225 ms
Wall time: 260 ms

due to vectorized matching. However, the latter is more memory intensive. The memory usage can be reduced by entirely ignoring the interior facets via MeshTet.load('labelled.msh', ignore_interior_facets=True.

Fixes #1049.

[Vinc0110]

It would be nice to speed up the mesh loading from labeled gmsh files, which also take a very long time in my cases (sometimes several minutes).

Testing this new code with ignore_orientation=True, I get an error, unfortunately:

File "/usr/local/lib/python3.8/dist-packages/skfem/io/meshio.py", line 134, in from_meshio
    boundaries[k] = np.nonzero((a == b[:, None]).all(axis=2).any(axis=1))[0]
AttributeError: 'bool' object has no attribute 'all'

I'm using Python 3.8 with numpy 1.24.4.

[Vinc0110]

It works great with Python 3.10. Huge speed improvement (about 10x). Thanks a lot!