feat: remove List.new(_) constructor and consolidate into List.filled(_,_)

Remove the List.new(_) primitive that initialized a list with null elements, merging its functionality into List.filled(_,_) which now accepts both size and default value. Add validation for negative size with a clear error message, and introduce comprehensive test coverage for filled list creation including edge cases for negative size, non-integer size, and non-numeric size arguments.

test/core/list/filled.wren

@@ -0,0 +1,8 @@
+var list = List.filled(3, "value")
+System.print(list.count) // expect: 3
+System.print(list) // expect: [value, value, value]
+
+// Can create an empty list.
+list = List.filled(0, "value")
+System.print(list.count) // expect: 0
+System.print(list) // expect: []

test/core/list/filled_size_negative.wren

@@ -0,0 +1 @@
+List.filled(-1, null) // expect runtime error: Size cannot be negative.

test/core/list/filled_size_not_int.wren

@@ -0,0 +1 @@
+List.filled(1.2, null) // expect runtime error: Size must be an integer.

test/core/list/filled_size_not_num.wren

@@ -0,0 +1 @@
+List.filled("not num", null) // expect runtime error: Size must be a number.

test/core/list/new_extra_args.wren

@@ -1,8 +0,0 @@
-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]