fix bug in parse_n

I initially wrote this for 10 elements in the octopi flashing grid
puzzle, which is why I had a 10 in there, even though I did have the
const N already. Here I rewrote it slightly, because with `try_into`
already doing a length check, mine was redundant anyway.

src/parsing.rs

@@ -42,12 +42,11 @@ pub fn parse_n<T: Debug, P: Tokens<Item = char>, const N: usize>(
     parser: &dyn Fn(&mut P) -> Option<T>,
     separator: &dyn Fn(&mut P) -> bool,
 ) -> Option<[T; N]> {
-    let elements: Vec<T> = tokens.sep_by(parser, separator).collect();
-    if elements.len() != 10 {
-        None
-    } else {
-        Some(elements.try_into().unwrap())
-    }
+    tokens
+        .sep_by(parser, separator)
+        .collect::<Vec<T>>()
+        .try_into()
+        .ok()
 }
 
 #[cfg(test)]