prod test vectors failing likely due to key split

[unnawut]

Prod test vectors are still failing although for a different reason: "Error: The operation was canceled." without more description.

I think this is similar to #355 because with the proposal/attestation key split in #449 we're doubling the keys in memory so they're going OOM again.

Prefer to not limit the number of workers so that we always fully utilize the test infra

ref: https://github.com/leanEthereum/leanSpec/actions/runs/23190229785/job/67514064289