Tests

Refactor test_smooth for pytest #1050

Job	Run time
Fedora	17m 7s
Shared, release	18m 9s
Debug, shared	23m 8s
Optimised, static	14m 3s
Default options, Ubuntu 22.04	12m 22s
PETSc unreleased, ADIOS2, 3D metrics	27m 40s
Shared, OpenMP, 3D metrics	13m 51s
	2h 6m 20s

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