Create advent prelude and cleanup lint by using it.

2021/src/day16.rs

@@ -1,14 +1,5 @@
-use std::{
-    fmt::{Debug, Error, Formatter},
-    io::Read,
-    num::ParseIntError,
-    ops::{Index, IndexMut},
-    str::FromStr,
-};
-
-use anyhow::Result;
-use aoc_runner_derive::{aoc, aoc_generator};
-use thiserror::Error;
+use advent::prelude::*;
+use aoc_runner_derive::aoc;
 
 fn hex(b: &u8) -> u8 {
     if *b >= b'A' {