To use anything like crucifixion to punish a criminal would be unthinkable in Christian Europe. Perhaps the film makers used Japanese models, where it was extensively used in Traditional Japan.
There is no significant link between medieval witchcraft and French Republicanism. Witchcraft normally had male leaders. Republicanism was based on Enlightenment Rationalism and scorned anything magic.
The end of the film references the French Revolution of 1789, but then an image is shown of Eugène Delacroix's famous painting "Liberty Leading the People." That painting - "Liberty Leading the People" - depicts the July Revolution of 1830, not the French Revolution of 1789.