Add timestamp and is_full_visit bit to ori->snp edges' label

Resolves #4780 (closed)

cc @zack @seirl @olasd

Please voice your criticism of the gRPC API and bit layout now, because it is going to be hard to change them after we release the next graph.

I am probably going to change the Rust API to make it emit the EdgeLabel enum instead of UntypedEdgeLabel when possible, if I can wrangle the type checker to do it when node types are loaded (unsuccessfully so far)