Speed: Too many http calls to getInfo and getBlock in pushTransactions

[n13]

Currently trying to solve very slow transaction speed for push transactions on EOS Dart, so these are just some inefficiencies that I found. Investigating further

Multiple redundant calls into chain

• pushTransactions calls getInfo and getBlock, then calls _pushTransactionArgs
• _pushTransactionArgs calls getRequiredKeys
• getRequiredKeys calls getInfo and getBlock again

It would be better to pass around info and block objects since this all happens inside one pushTransactions call