Bugfix: Hellfire "Life to mana" and "Mana to life"

[kphoenix137]

Fixes: https://github.com/diasurgical/devilutionX/issues/6875

Hellfire writes the Life and Mana directly to the item. This is a problem since it does not dynamically change the values, but keeps the values from when the item is originally generated. This becomes less of a problem the more frequently the item with one of these powers is regenerated, however it is a terrible way of doing it.

This PR rather sets the Life and Mana values dynamically so they stay accurate to the item description.