This commit adds CrdsEntry trait which allows generic lookups into crds
table. For example to get ContactInfo or LowestSlot associated with a
Pubkey, the lookup code would be respectively:
crds.get::<&ContactInfo>(pubkey)
crds.get::<&LowestSlot>(pubkey)
* Move gossip modules to solana-gossip
* Update Protocol abi digest due to move
* Move gossip benches and hook up CI
* Remove unneeded Result entries
* Single use statements