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/abs.wren

@@ -1,6 +1,6 @@
-io.write(123.abs)    // expect: 123
-io.write(-123.abs)   // expect: 123
-io.write(0.abs)      // expect: 0
-io.write(-0.abs)     // expect: 0
-io.write(-0.12.abs)  // expect: 0.12
-io.write(12.34.abs)  // expect: 12.34
+IO.write(123.abs)    // expect: 123
+IO.write(-123.abs)   // expect: 123
+IO.write(0.abs)      // expect: 0
+IO.write(-0.abs)     // expect: 0
+IO.write(-0.12.abs)  // expect: 0.12
+IO.write(12.34.abs)  // expect: 12.34