keep spammers funded in background

[zeroXbrock]

Is your feature request related to a problem? Please describe.

For long-running spammers (esp. when passing --forever) the spammer accounts will eventually run out of ETH, and the spammer's txs will cease to land. In most devnet scenarios, the account that funded the spammers will have tons of ETH (10,000), and will be able to fund the spammer accounts for several days before it runs out.

Describe the solution you'd like

Add a new task that runs in the background while spamming, which funds the accounts periodically.

The period at which the accounts should be funded should be just less than the time it takes for them to run out of ether by spamming. --min-balance, get_max_spam_cost(), and --tps/--tpb should be sufficient to calculate this period.

[0xl3on]

ooh this is a quite good idea! not sure if you already took it, if not i can do it!