List a new marketplace item (restricted to listing creator)
fn list_item(
env: soroban_sdk::Env,
creator: soroban_sdk::Address,
item_id: u64,
price: i128,
token_contract: soroban_sdk::Address,
)Initialize the marketplace admin and fee address
fn initialize(
env: soroban_sdk::Env,
admin: soroban_sdk::Address,
platform_fee_address: soroban_sdk::Address,
)Buy an item. Splits purchase price: 90% to creator, 10% platform fee.
fn purchase_item(env: soroban_sdk::Env, buyer: soroban_sdk::Address, item_id: u64)