chore: convert to cargo workspace with four crates

crates/xy-protocol/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "xy-protocol"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+
+[dependencies]
+serde.workspace = true
+serde_json.workspace = true
+thiserror.workspace = true
+kdl.workspace = true
+humantime.workspace = true
+humantime-serde.workspace = true
+
+[dev-dependencies]
+tempfile.workspace = true

crates/xy-protocol/src/lib.rs

@@ -0,0 +1 @@
+//! Wire types and config schema shared between the xy daemon and CLI.