Fix duration of fire and cold protection spells

- Respect duration from scripts for fire spells
- Reduce default duration for NPCs from 2000000ms to 20000ms for both

This way the better match the armor and lower armor spells.

Notes:

1. Scripts never specify a duration for cold_protection.
2. Scripts always specify a duration of 10000 for fire protection
   (this was previously ignored), except for one case.