## Issue Addressed NA ## Proposed Changes Reduces allocations by initializing the `pubkeys` vec to its final size. I doubt this will make a substantial difference, but it's nice to do it this way. Seeing as `indexed_attestation.attesting_indices` has a [fixed length](https://github.com/sigp/lighthouse/blob/e4b62139d7e2d5b0499648663af8de25b368f0bd/consensus/types/src/indexed_attestation.rs#L22), there's no real risk of a memory blow-up by pre-allocating the size of the `Vec`. ## Additional Info NA