Broken Ethereum committee change proof

[tchataigner]

While testing for the new bls crate commit, I noticed that both our benchmark and test for committee change proof generation seemed to be broken.

I do not get yet why they fail as they work up until commit c9293b3 (#165), and all that PR does is update deps to sphinx dev (sphinx#152, 93e4598).

The command ran were:

# Goes on forever
zk-light-clients/ethereum/light-client$ cargo +nightly-2024-08-13 nextest run --verbose --release --profile ci --all-features --package ethereum-lc --no-capture --run-ignored all -- proofs::committee_change::test

# Both proof test are failing with SIGSEV
zk-light-clients/ethereum/light-client$ RUST_LOG=debug cargo +nightly-2024-08-13 nextest run --verbose --release --profile ci --all-features --package ethereum-lc --no-capture --run-ignored all -- proofs::committee_change::test

I discovered it on the branch feature/update-bls-version that updates our deps to the latest update of the bls crate.