make sure that the RNG is in a reproducible state for every single test

test/common.py

test/test_energy_gradients.py

test/test_field.py

test/test_gaussian_energy.py

test/test_kl.py

test/test_linearization.py

test/test_minimizers.py

test/test_multi_field.py

test/test_operators/test_adjoint.py

test/test_operators/test_composed_operator.py

test/test_operators/test_convolution_operators.py

test/test_operators/test_correlated_fields.py

test/test_operators/test_diagonal_operator.py

test/test_operators/test_fft_operator.py

test/test_operators/test_harmonic_transform_operator.py

test/test_operators/test_interpolated.py

test/test_operators/test_jacobian.py

test/test_operators/test_nft.py

test/test_operators/test_partial_multifield_insert.py

test/test_operators/test_regridding.py