Support fast blocks

[thewhaleking]

The new btcli should support fast blocks. It currently does not.

[thewhaleking]

This might be something with nonces

[thewhaleking]

The issue is that the work hashes are only valid for 3 blocks. Current implementation is 10-15 blocks in time spent. I've been able to speed this up quite a bit, but I can't seem to go faster than 5 blocks.

[thewhaleking]

This will help for faucet: opentensor/subtensor#944

[thewhaleking]

#245