Use batch signature verification for block signatures

[vihu]

This changes block signature verification to use batch functionality from libp2p_crypto. In my testing it shows roughly 4-6x faster signature verification.

Furthermore it alters the signature verification to ensure that the signees are unique. All other checks are the same. I have been able to resync OK with this but someone else may also wanna try.

TODO:

• [ ] Switch libp2p and libp2p_crypto branches back to master when their base PRs merge