Replace load_module() usage

[bilderbuchi]

Tests on Python 3.10 show a deprecation warning

 tests/experiment/test_procedure.py::test_procedure_wrapper
tests/experiment/test_results.py::test_procedure_wrapper
  <frozen importlib._bootstrap>:283: DeprecationWarning: the load_module() method is deprecated and slated for removal in Python 3.12; use exec_module() instead

load_module() is used in experiment in ProcedureWrapper.__setstate__ and results.__setstate__.
This seems to be the way to replace this. However, possibly the replacement could not be that straightforward, so care needs to be taken to confirm everything still works as expected, maybe with some added tests.

Luckily, we have until Python 3.12, so there is some time :D