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/number/mod.wren

@@ -1,14 +1,14 @@
-io.write(5 % 3) // expect: 2
-io.write(10 % 5) // expect: 0
-io.write(-4 % 3) // expect: -1
-io.write(4 % -3) // expect: 1
-io.write(-4 % -3) // expect: -1
-io.write(-4.2 % 3.1) // expect: -1.1
-io.write(4.2 % -3.1) // expect: 1.1
-io.write(-4.2 % -3.1) // expect: -1.1
+IO.write(5 % 3) // expect: 2
+IO.write(10 % 5) // expect: 0
+IO.write(-4 % 3) // expect: -1
+IO.write(4 % -3) // expect: 1
+IO.write(-4 % -3) // expect: -1
+IO.write(-4.2 % 3.1) // expect: -1.1
+IO.write(4.2 % -3.1) // expect: 1.1
+IO.write(-4.2 % -3.1) // expect: -1.1
 
 // Left associative.
-io.write(13 % 7 % 4) // expect: 2
+IO.write(13 % 7 % 4) // expect: 2
 
 // TODO: Unsupported RHS types.
 // TODO: Error on mod by zero.