Lido: ↩️ 4⃣ Negative rebase sanity check w/ pluggable second opinion

Improving Lido protocol security by protecting against possible malicious negative rebase manipulations.

https://snapshot.org/#/lido-snapshot.eth/proposal/0xa44f6a4dba07d7e24b0e4180025f7a9db6251046daa74d2a8fae84de0d9ce21e