Protocol types, codec, handler trait, and client for the Trustless key provider protocol.

This crate implements the communication protocol between the Trustless proxy and key provider processes. Key providers hold TLS private keys and perform signing operations on behalf of the proxy, communicating over stdin/stdout with length-delimited JSON messages.

For key provider implementors

Implement the [handler::Handler] trait and call [handler::run] to start the event loop. See trustless-provider-filesystem for a complete example.

For proxy internals

Use [client::ProviderClient] to communicate with a spawned provider process.