Implement weak subjectivity safety checks

[dapplion]

See

• Electra: Update WS period computation ethereum/consensus-specs#4179

[michaelsproul]

We don't have this calculation implemented anywhere for us to update 😄

[michaelsproul]

I think we can close this @dapplion?

[dapplion]

We don't have this calculation implemented anywhere for us to update 😄

WOT why? We should. If the user tries to start LH with an existing DB outside the WS period we should at least log a big warning and ideally exit unless there's a flag.

[michaelsproul]

Yeah, agree we should. I think it just never got done. When we originally implemented checkpoint sync I don't think there was a spec for the weak subj period calculation