[security] MinRoot delay function is "vulnerable"

[mrain]

Existing attacks break the delay property of MinRoot function. However, currently it costs dozens of millions to launch such an attack.

Since we do not care about verifiability, we could simply switch to a hash chain for our delay function.

Ref:

• https://ethresear.ch/t/statement-regarding-the-public-report-on-the-analysis-of-minroot/16670
• https://crypto.ethereum.org/events/minrootanalysis2023.pdf