feat: use checked Day type instead of integers for days (#35)

src/template/commands/read.rs

@@ -1,8 +1,9 @@
 use std::process;
 
 use crate::template::aoc_cli;
+use crate::Day;
 
-pub fn handle(day: u8) {
+pub fn handle(day: Day) {
     if aoc_cli::check().is_err() {
         eprintln!("command \"aoc\" not found or not callable. Try running \"cargo install aoc-cli\" to install it.");
         process::exit(1);