Extension trait surface for Velo.
Out-of-tree implementors of Transport,
FrameTransport, and
PeerDiscovery depend on this crate. It
contains the trait definitions and the value/error types that appear in
their signatures — nothing more. Anyone who only uses Velo should depend
on the velo crate; only plugin authors should reach for velo-ext.
Stability
This crate is the contract that downstream impls compile against. New trait
methods land with default impls; signature changes require a deliberate
version bump coordinated with velo. See Cargo.toml for the full policy.