You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: idempotency_token.rs
    path of file: ./repos/aws-sdk-rust/sdk/braket/src
    
    the code of the file until where you have to start completion: // Code generated by software.amazon.smithy.rust.codegen.smithy-rs. DO NOT EDIT.
/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */

use aws_smithy_types::config_bag::{Storable, StoreReplace};
use std::sync::Mutex;

pub(crate) fn uuid_v4(input: u128) -> String {
    let mut out = String::with_capacity(36);
    // u4-aligned index into [input]
    let mut rnd_idx: u8 = 0;
    const HEX_CHARS: &[u8; 16] = b"0123456789abcdef";

    for str_idx in 0..36 {
        if str_idx == 8 || str_idx == 13 || str_idx == 18 || str_idx == 23 {
            out.push('-');
        // UUID version character
       
    
pub(crate) fn uuid_v4(input: u128) -> String {
    let mut out = String::with_capacity(36);
    // u4-aligned index into [input]
    let mut rnd_idx: u8 = 0;
    const HEX_CHARS: &[u8; 16] = b"0123456789abcdef";

    for str_idx in 0..36 {
        if str_idx == 8 || str_idx == 13 || str_idx == 18 || str_idx == 23 {
            out.push('-');
        // UUID version character
        } else if str_idx == 14 {
            out.push('4');
        } else {
            let mut dat: u8 = ((input >> (rnd_idx * 4)) & 0x0F) as u8;
            // UUID variant bits
            if str_idx == 19 {
                dat |= 0b00001000;
            }
            rnd_idx += 1;
            out.push(HEX_CHARS[dat as usize] as char);
        }
    }
    out
}