Fix Dockerfile: copy benches/ dir so Cargo.toml bench entry resolves

products/01-llm-cost-router/Dockerfile

@@ -4,6 +4,7 @@ WORKDIR /app
 RUN apt-get update && apt-get install -y pkg-config libssl-dev && rm -rf /var/lib/apt/lists/*
 COPY Cargo.toml Cargo.lock* ./
 COPY src/ src/
+COPY benches/ benches/
 RUN cargo build --release
 
 FROM debian:bookworm-slim