Function verify_transactions 

pub async fn verify_transactions(
    overlay: &BlockchainOverlayPtr,
    verifying_block_height: u32,
    block_target: u32,
    txs: &[Transaction],
    tree: &mut MerkleTree,
    verify_fees: bool,
) -> Result<(u64, u64)>

Verify a set of Transaction in sequence and apply them if all are valid. In case any of the transactions fail, they will be returned to the caller as an error. If all transactions are valid, the function will return the total gas used and total paid fees from all the transactions. Additionally, their hash is appended to the provided Merkle tree.

Note: Always remember to purge new trees from the database if not needed.