Take into account the actually used gas by the transactions and fetch more transaction

[xgreenx]

Beta 3 and upcoming beta 4 suffer the problem with transactions with a 10M gas limit, but the actual used gas is 5K. TX pool only returns 50 transactions because the max gas limit of the block is 500M. It decreases the tps of the blockchain, and users can't commit a lot of transactions.

We need to update the transaction selection logic to be a stream like in #1206. This issue tracks only the streaming implementation of the transaction selection, and the soft commit part should be done during the parent issue.

Also, we need to patch the latest 0.17 and 0.18 releases with this fix.

During development, we need to consider that this stream will be later used during parallel execution.