vectorization: improve treatment of unary minus
Changes in !48 (merged) caused test failures in https://i10git.cs.fau.de/pycodegen/lbmpy/-/jobs/534348.
Also add a test for vectorized unary minus and sp.Abs, suppress a warning with older versions of randomgen and make double-precision vector RNG accurate on Clang in fast-math mode.
The errors in test_resting_fluid and test_point_force are fixed by lbmpy!63 (merged). The error in test_phi_staggered_equivalence_on_random is fixed by https://i10git.cs.fau.de/pycodegen/pygrandchem/-/merge_requests/4.