Run flake8 in Github CI on target Py version

Add missing use_kwargs in memoize for _make_dep_mapper

Handle constant values in interior_trace_pair and cross_rank_trace_pairs

Fix possible nan eoc in test_mass_surface_area

test downstream projects

Fixes #44.

Fix normals for empty boundary

Test that normal DOFArrays for empty boundaries have the same number of groups as the corresponding discretization

Simply meshmode.mesh.generation imports

CI/README: master->main

Fix stringifier dispatch for Operator subclasses

Make reference diff use elwise_linear loopy kernel

Install instructions: add --editable

Remove hwloc processing for Conda Gitlab CI

See merge request inducer/grudge!96

Pin Github CI to libhwloc 2