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()`.
Add a new test file `test/constructor/infix_class_expression.wren` that verifies
the ability to use an infix operator on a freshly constructed object instance.
The test creates a `Foo` class with a `+` method and checks that `new Foo + "value"`
correctly evaluates to `"Foo value"`. Also includes a TODO comment noting other
constructor expression patterns that should be tested.