feat: implement list literal syntax and List class with count property

Add support for list literals in the compiler with bracket-delimited syntax and comma-separated elements. Introduce the ObjList runtime type with a contiguous elements array, garbage collection marking, and proper memory deallocation. Expose a `List` class in the core library with a `count` method returning the number of elements. Update the grammar table to register `[` as a prefix token for list compilation instead of an infix subscript operator, and reorder opcode enum entries to place CODE_LIST before the load/store group.

test/class_inheritance.wren

@@ -24,3 +24,4 @@ bar.method(1, 2, 3, 4) // expect: bar
 // TODO(bob): Private fields.
 // TODO(bob): Super (or inner) calls.
 // TODO(bob): Grammar for what expressions can follow "is".
+// TODO(bob): Prevent extending built-in types.

test/list_count.wren

@@ -0,0 +1,7 @@
+io.write([].count)           // expect: 0
+io.write([1].count)          // expect: 1
+io.write([1, 2, 3, 4].count) // expect: 4
+
+// TODO(bob): Literal syntax, including newline handling.
+// TODO(bob): Unterminated list literal.
+// TODO(bob): Subscript operator.