refactor: convert IO from singleton instance to static class with metaclass native methods

Replace the global `io` singleton object with a static `IO` class, moving the `write` native from the instance to the metaclass. Update all benchmark, example, and test files to use `IO.write()` instead of `io.write()`.

test/list/newlines.wren

@@ -8,7 +8,7 @@ var list = [
 
 ]
 
-io.write(list[0]) // expect: a
-io.write(list[1]) // expect: b
-io.write(list[2]) // expect: c
-io.write(list[3]) // expect: d
+IO.write(list[0]) // expect: a
+IO.write(list[1]) // expect: b
+IO.write(list[2]) // expect: c
+IO.write(list[3]) // expect: d