Reference data for OP Stack wire formats that specify an "unsigned Base128 varint, as defined in
protobuf spec" — span-batch uvarint fields, and the opstack ENR entry.
op-node decodes both with Go's standard library encoding/binary.ReadUvarint. Any Rust decoder
used on the same bytes must accept exactly the same set, or the two clients disagree on
identical input. Background: ethereum-optimism/protocol-team#223, fixed for span batches in
ethereum-optimism/optimism#22126.