fix: Use built-in RNG (#1599)

### Summary

.NET 8 supports Xoroshiro 256** off the shelf and added Shuffle. Switching to that implementation.

### Developer Notes

* Removed many convenience methods that weren't used.

Projects/UOContent/Commands/ResetRng.cs

@@ -15,6 +15,6 @@ public class ResetRng
     )]
     private static void ResetRng_OnCommand(CommandEventArgs e)
     {
-        RandomSources.SetRng(new Xoshiro256PlusPlus());
+        BuiltInRng.Reset();
     }
 }