Migrate to pytest

Dockerfile

test/common.py

test/test_energies/test_consistency.py

test/test_energy_gradients.py

test/test_field.py

test/test_gaussian_metric.py

test/test_minimization/test_minimizers.py

test/test_minimizers.py

test/test_model_gradients.py

test/test_models/test_model_gradients.py

test/test_multi_field.py

test/test_operators/__init__.py

test/test_operators/test_adjoint.py

test/test_operators/test_composed_operator.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_regridding.py

test/test_operators/test_smoothing_operator.py

test/test_spaces/__init__.py