generate_gmsh(): Set target_unit in GmshRunner to avoid deprecation warning

See merge request inducer/meshmode!59

Break up `connection/__init__.py`

Closes #11

See merge request inducer/meshmode!57

Reverse Chained Connection

See merge request !51

return mesh from refine_uniformly

See merge request inducer/meshmode!56

Better error messsages when asking about orientation of non-volume meshes

See merge request inducer/meshmode!55

Tweak object array treatment in separate_by_real_and_imag

See merge request inducer/meshmode!53

Avoid on-the-fly gmsh generation, to avoid flaky CI--e.g....

See merge request inducer/meshmode!52

Avoid on-the-fly gmsh generation, to avoid flaky CI--e.g. https://gitlab.tiker.net/inducer/meshmode/-/jobs/69357)