Update rewards.go

This pull request is meant to adjust the staking exponent from 0.9 to 0.75 to create a more equitable reward distribution again and align the network's incentives with broader participation and security goals that way.

Rationale:

1. 0.75 Stakeweight – Making Newbies Mining Great Again:

A lower staking exponent provides relatively higher rewards to smaller stakeholders, fostering participation among new and smaller miners. This change supports the inclusivity principle at the core of the Idena network.

2. Voluntarily Punishing Top 100 Stakers:

Many of the top 100 stakers have significantly reduced their contributions to the community, some by even ceasing to create flips. The argument for higher engagement due to higher stake didn't play out well enough, so why reward them for passivity? By reducing their disproportionate advantage, this change disincentivizes passive large stakes while rewarding active network participants. It might also contribute to the repopulation of pools, but that doesn't need to harm decentralisation at all, as long as we punish bad flips, as long as we have many different poolowners and not just two or three of them. 



3. Improved Security Contributions:

Smaller, active stakers often contribute to the network’s security by actively participating in validations. Realigning rewards toward these contributors strengthens the network’s overall security.



4. Vitalik’s Sublinear Staking Principle:

This approach aligns with Vitalik Buterin’s proposal for sublinear staking as outlined in the Ethereum Research repository. A sublinear staking mechanism discourages excessive centralization of staking power and promotes a healthier, more decentralized network. We just have to find the perfect middleground. It seems that 0.9 didn't deliver enough engagement yet?

blockchain/rewards.go

@@ -38,7 +38,7 @@ func rewardValidIdentities(appState *appstate.AppState, config *config.Consensus
 
 func stakeWeight(stake *big.Int) float32 {
 	stakeF, _ := ConvertToFloat(stake).Float64()
-	return float32(math2.Pow(stakeF, 0.9))
+	return float32(math2.Pow(stakeF, 0.75))
 }
 
 func addSuccessfulValidationReward(appState *appstate.AppState, config *config.ConsensusConf,