Marketplace Contract Implementation

[geofmureithi]

Objective: Develop a marketplace smart contract with fundamental methods to facilitate asset listing, buying, updating, and cancellation.

Methods:

1. init(admin: Address, percentage: i128): Initialize the contract with the admin's address and a percentage for the admin fee.
2. list_asset(seller: Address, asset: Address, price: i128): Allow sellers to list assets by specifying the seller's address, the asset's address, and the asset's price.
3. buy_asset(buyer: Address, asset: Address, price: i128): Enable buyers to purchase assets by providing the buyer's address, the asset's address, and the agreed-upon price.
4. update_listing(seller: Address, asset: Address, old_price: i128, new_price: i128): Permit sellers to update the price of a listed asset, ensuring they provide the correct seller and asset addresses, as well as the old and new prices.
5. cancel_listing(seller: Address, asset: Address, price: i128): Allow sellers to remove a listing by specifying their address, the asset's address, and the price at which it was listed.

Checklist:

• [x] Scope
• [x] Implementation
• [x] Integration Tests
• [ ] Documentation

[geofmureithi]

@mariopil @eloylp Let me hear any thoughts and suggestions.

[eloylp]

82 Was reviewed and approved - with pending impl at #90 - closing this - re-open if necessary.