Refactor avatar skilldepot and constellation/talent changing

Ensures Traveler retains talent levels and constellations on inactive elements when switching elements.
Relevant for any other skillDepot-changing activities like Windtrace too, though keeping those in the db might not be as useful.

Refactor avatar talent upgrade and access
Refactor skillExtraCharges

src/main/java/emu/grasscutter/server/packet/recv/HandlerAvatarSkillUpgradeReq.java

@@ -13,8 +13,10 @@ public class HandlerAvatarSkillUpgradeReq extends PacketHandler {
     public void handle(GameSession session, byte[] header, byte[] payload) throws Exception {
         AvatarSkillUpgradeReq req = AvatarSkillUpgradeReq.parseFrom(payload);
 
+        // Sanity checks
+        var avatar = session.getPlayer().getAvatars().getAvatarByGuid(req.getAvatarGuid());
+        if (avatar == null) return;
         // Level up avatar talent
-        session.getServer().getInventorySystem().upgradeAvatarSkill(session.getPlayer(), req.getAvatarGuid(), req.getAvatarSkillId());
+        avatar.upgradeSkill(req.getAvatarSkillId());
     }
-
 }