fix: Fixes mount stamina, adds Pub46+ Ethereal stamina (#1716)

### Summary
* Makes mount stamina significantly faster.
* Reduces absolute reset from 24 hours to 4 hours.
* Adds Pub 46+ Ethereal stamina where the stamina is global to all mounts for the player
* Removes serialization of stamina entirely because it's ok if it gets reset during shard restarts.

Projects/UOContent/Mobiles/BaseCreature.cs

@@ -4293,7 +4293,8 @@ namespace Server.Mobiles
                 if (stamGain > 0)
                 {
                     Stam += stamGain;
-                    // 64 food = 3,640 steps
+
+                    // 61 food = 3,840 steps
                     StaminaSystem.RegenSteps(this as IHasSteps, stamGain * 4);
                 }