test(pipeline): convert risk-neutrality tests from pytest to unittest

CI uses 'unittest discover' which doesn't have pytest available.
pytest.approx -> assertAlmostEqual, pytest.raises -> assertRaises.
Includes the test_factors/test_pipeline/test_pipeline_engine and
phase-2/3 conversions cherry-picked from PRs coding-kitties#506 and coding-kitties#508.

Author: MDUYN