fix: Fixes poison field duration, cleans up skill calculations and poison calculations (#1582)

### Summary
- [X] Fixes poison field duration
- [X] Adds SA+ poison spell calculations
- [X] Cleans up skill calculations
- [X] Adjusts poison level thresholds to properly reflect OSI

Projects/UOContent/Misc/RegenRates.cs

@@ -79,7 +79,7 @@ namespace Server.Misc
 
             if (AnimalForm.UnderTransformation(from, typeof(Dog)) || AnimalForm.UnderTransformation(from, typeof(Cat)))
             {
-                points += from.Skills.Ninjitsu.Fixed / 30;
+                points += (int)(from.Skills.Ninjitsu.Value / 3);
             }
 
             return TimeSpan.FromSeconds(10.0 / (1 + points));