Quest config nullability and documentation (Part 2) (#415)

* Make Interp1 generic

* Finish quest controller nullability fixes

* More model and nullability improvements and fixes

* Rename `specificLocationChance`

* rename `bodyPartChance`

* finish comments

Libraries/SPTarkov.Server.Core/Controllers/RepeatableQuestController.cs

@@ -810,7 +810,7 @@ public class RepeatableQuestController(
         foreach (var target in targetsConfig)
         {
             // Target is boss
-            if (target.Data.IsBoss.GetValueOrDefault(false))
+            if (target.Data?.IsBoss ?? false)
             {
                 questPool.Pool.Elimination.Targets.Add(
                     target.Key,