feat(frontend): add live TPS and transaction count tracker - #37

jake said:

it can be done with the current events we're subscribing to. pseudocode would look something like this

let txCount = 0

const onTxnHeaderStart = (event) => {
    ++txCount;
    // ...
}

setInterval(() => {
    console.log('TPS:', txCount);
    txCount = 0;
}, 1000);