feat: add List.map method with test for element transformation

Implement a `map` method on the List class that applies a given function `f` to each element, returning a new list with the transformed values. Includes a test case verifying incrementing each element by 1.

builtin/core.wren

@@ -16,4 +16,12 @@ class List {
     }
     return result
   }
+  
+  map (f) {
+    var result = []
+    for (element in this) {
+      result.add(f.call(element))
+    }
+    return result
+  }
 }