Slice-Length Operation causes `not implemented` error in mles_product_sum

When attempting to run a Jolt guest to prove properties of image files (e.g., file-type checks or simple byte-pattern checks), I encountered errors during the proving phase. Several different guest operations were tested, but the Jolt prover consistently panicked with multiple occurrences of: `thread '<unnamed>' panicked at jolt-core/src/subprotocols/mles_product_sum.rs:186:14: not implemented` Just a slice length check also causes this error. ### Minimal Guest Example ```rust #![cfg_attr(feature = "guest", no_std)] #[jolt::provable(memory_size = 10240, max_trace_length = 65536, max_input_size = 10000, max_output_size = 10000)] fn check_jpeg(file_bytes: &[u8]) -> bool { file_bytes.len() > 0 } ``` ### Minimal Host ```rust use std::fs; pub fn main() { let target_dir = "/tmp/jolt-guest-targets"; let mut program = guest::compile_check_jpeg(target_dir); let prover_preprocessing = guest::preprocess_prover_check_jpeg(&mut program); let verifier_preprocessing = guest::verifier_preprocessing_from_prover_check_jpeg(&prover_preprocessing); let prove_check_jpeg = guest::build_prover_check_jpeg(program, prover_preprocessing); let verify_check_jpeg = guest::build_verifier_check_jpeg(verifier_preprocessing); let file_path = "example_flower.jpg"; let bytes = fs::read(file_path).expect("failed to read file"); let (output, proof, io_device) = prove_check_jpeg(&bytes); let is_valid = verify_check_jpeg(&bytes, output, io_device.panic, proof); println!("output: {output}"); println!("valid: {is_valid}"); } ``` Some cases also included the following: `thread 'main' panicked at jolt-core/src/poly/opening_proof.rs:904:51: called 'Option::unwrap()' on a 'None' value` Jolt commit: `88821842c` Hardware: M4 Mac Pro