Limit staking parameter changes

[dantaik]

Staking parameters are currently adjustable at will by stakers/provers. This encourages short-term competition, with provers constantly adjusting their parameters based on others' values. To discourage this reactive behavior and promote long-term stability, I suggest limiting parameter changes to once per week or day. This will ensure provers' staking parameters better reflect their actual proving capacity and costs, avoiding potentially harmful competition.

Another desired feature is to somehow encourage provers to submit proofs ASAP. This feature remains to be discussed and potential implemented.