Fixed exercises with a maximum number of transaction requirement

[l4n0r]

Some challenges enforce a maximum number of transactions, which is tracked using Foundry's vm.getNonce.

While the current approach uses vm.startPrank to simulate player transactions, this method only sets msg.sender and tx.origin — it does not increment the sender's nonce for each transaction (except for contract creations). As a result, nonce-based checks are not effective in counting regular transactions.

Foundry provides vm.startBroadcast, which is specifically designed to simulate real transactions that do increment the nonce. This pull request replaces vm.startPrank with vm.startBroadcast (only for the selected challenges) to more accurately enforce transaction count limits.