add a new pet that trades with players

New Mob Concept for Minecraft
a tamable companion mob designed to act like a personal merchant assistant, This mob introduces new interactive features for both singleplayer and multiplayer experiences, blending farming, trading, and automation in a friendly, pet-like way.

Functionality Modes:
1. Owner only:

• the mob uses a barrel as its bed and workstation.
• You decide what you want to sell to the mob (but not all items "tradeables up to Mojang").

Setup process:

• Place an item frame on or near the barrel and insert the item you want to sell to the mob.
• Fill the barrel with the item that the mob requires in return (the mob's preferred trade item – chosen by the game, not the player).
• the mob will search nearby for the required item (e.g., from farms, or dropped items).
• Once it gathers enough of the required item, it deposits it in the barrel and takes the item it wants in return.
• Over time, the mob levels up, unlocking more complex or efficient trades

2. Multiplayer:

• you can assign the mob to act as a shopkeeper or collector:
• You can choose what the mob will buy from or sell to other players.
• Other players can interact with the mob to trade items based on your setup.

Think of it like a personal economy system between you and your pet. You're selling something, and the mob "buys" it from you using its own preferred currency – with some automation thrown in.