replace array with an actual struct now that we have them

examples/puzzles/euler_16.zr

@@ -1,10 +1,10 @@
 func main[] : i64
-    let n: array = []
+    let n: Array = []
     array.push(n, 1)
 
     for j in 0..1000
         let carry = 0
-        for i in 0..array.size(n)
+        for i in 0..n->size
             let tmp: i64 = array.nth(n, i) * 2 + carry
             array.set(n, i, tmp % 10)
             carry = tmp / 10
@@ -13,7 +13,7 @@ func main[] : i64
             carry = carry / 10
     
     let sum = 0
-    for i in 0..array.size(n)
+    for i in 0..n->size
         sum = sum + array.nth(n, i)
 
     io.println_i64(sum)