This PR includes changes required for delhi hard fork schedule at block
`29638656` on mumbai testnet. It changes few major parameters.
1. Sprint length - the number of bor blocks post which a new validator
mines has been reduced from 64 to 16.
2. Block time - the block time which was increased earlier for some
experiments to 5 seconds has been reduced to 2 seconds (along with
backup multiplier and producer delay).
3. Base fee denominator - this fields has been increased from 8 to 16 to
smoothen the effect of EIP 1559.
