fix: tighten consensus auxiliary inputs

[andrewnguyen22]

A few small consensus hardening changes that came out of the security review:

• ignore future or stale proposal timestamps when calculating process time
• count the signed vote before looking at optional attachments
• put basic size and iteration bounds on incoming VDFs
• keep consensus delivery direct and make sure the transport sender matches the message signer
• make sure post-election leader messages are actually signed by the elected proposer
• fully verify the QC at the sync tip before calling sync done
• require more than one-third voting power before pacemaker can jump rounds