collections: fix LinkedList.to_format

For-loop in LinkedList.to_format goes brrrrrr and prints the value of
the first node an infinte number of times because it does not properly
iterate the linked list.

Fix the list iterations and add the missing string format specifier.

Bug can be reproduced with:
```
import std;
fn void main() => @pool()
{
	io::printfn("%s", linkedlist::@tnew{usz}({1,2,3}));
}
```

lib/std/collections/linkedlist.c3

@@ -24,9 +24,9 @@ struct LinkedList
 fn usz? LinkedList.to_format(&self, Formatter* f) @dynamic
 {
 	usz len = f.print("{ ")!;
-	for (Node* node = self._first; node != null; node.next)
+	for (Node* node = self._first; node != null; node = node.next)
 	{
-		len += f.printf(node.next ? "%s, " : "s", node.value)!;
+		len += f.printf(node.next ? "%s, " : "%s", node.value)!;
 	}
 	return len + f.print(" }");
 }