Tests

Fix lots of clang-tidy issues in fv_ops #4173

Job	Run time
Fedora	19m 10s
CUDA	12m 46s
CMake, PETSc unreleased, ADIOS2	25m 34s
Default options, Ubuntu 20.04	17m 24s
Optimised, static	21m 4s
Debug, shared	24m 52s
Shared, release, Ubuntu 20.04	18m 13s
Shared, OpenMP, 3D metrics	15m 11s
CMake, new PETSc	17m 50s
Coverage	14m 3s
	3h 6m 7s

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