Router, add xrpc function interface, test in main

Adds an interface for adding xrpc queries and procedures that is a bit
simpler than directly interfacing with axum. Should provide good
scaffolding for next steps.

rust/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 
 [dependencies]
 axum = { version = "0.8.3", features = ["json"] }
+axum-macros = "0.5.0"
 serde = "1.0.219"
 serde_json = "1.0.140"
 sqlx = { version = "0.8.5", features = ["runtime-tokio"] }