feat: add List.new(_) and List.filled(_,_) constructors with size and default value

Add two new list constructors to the Wren VM: `List.new(size)` creates a list of given size with null elements, and `List.filled(size, value)` creates a list with all elements initialized to a specified default value. Includes corresponding C primitives `list_newWithSize` and `list_newWithSizeDefault`, registration in `wrenInitializeCore`, and a test file verifying both constructors produce correct counts and element values. Also adds Max Ferguson to AUTHORS.

test/core/list/new_extra_args.wren

@@ -0,0 +1,8 @@
+var list = List.new(5)
+
+System.print(list.count) // expect: 5
+System.print(list) // expect: [null, null, null, null, null]
+
+var list2 = List.filled(5, 2)
+System.print(list2.count) // expect: 5
+System.print(list2) // expect: [2, 2, 2, 2, 2]