Fix P1 Rust: use dd0c_route:: instead of crate:: in binary imports, add hex crate

Binary targets (api, proxy, worker) can't use crate:: to access lib modules.
Must reference the library crate name dd0c_route:: instead.

products/01-llm-cost-router/Cargo.toml

@@ -18,6 +18,7 @@ name = "dd0c-worker"
 path = "src/worker/main.rs"
 
 [dependencies]
+hex = "0.4.3"
 # Web framework
 axum = { version = "0.7", features = ["ws", "macros"] }
 tokio = { version = "1", features = ["full"] }