Extract a proto crate out of rpc (#12852)

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/rpc/src/rpc.rs

@@ -1,16 +1,15 @@
 pub mod auth;
 mod conn;
-mod error;
 mod extension;
 mod notification;
 mod peer;
 pub mod proto;
 
 pub use conn::Connection;
-pub use error::*;
 pub use extension::*;
 pub use notification::*;
 pub use peer::*;
+pub use proto::{error::*, Receipt, TypedEnvelope};
 mod macros;
 
 pub const PROTOCOL_VERSION: u32 = 68;