Harden strace benchmark binaries

Make the standalone protocol operation examples return and print concrete checksums derived from protocol state so the traced work cannot be optimized away as dead computation.

examples/protocol_op_decode_call.rs

@@ -3,6 +3,6 @@ mod common;
 
 fn main() {
     let iterations = common::iterations_from_args(1_000);
-    common::run_decode_call(iterations);
-    println!("decode_call iterations={iterations}");
+    let checksum = common::run_decode_call(iterations);
+    println!("decode_call iterations={iterations} checksum={checksum}");
 }