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/inheritance/inherit_fields.wren

@@ -5,8 +5,8 @@ class Foo {
   }
 
   fooPrint {
-    io.write(_field1)
-    io.write(_field2)
+    IO.write(_field1)
+    IO.write(_field2)
   }
 }
 
@@ -17,8 +17,8 @@ class Bar is Foo {
   }
 
   barPrint {
-    io.write(_field1)
-    io.write(_field2)
+    IO.write(_field1)
+    IO.write(_field2)
   }
 }
 

test/inheritance/inherit_methods.wren

@@ -1,15 +1,15 @@
 class Foo {
-  methodOnFoo { io.write("foo") }
-  method(a) { io.write("foo") }
-  method(a, b, c) { io.write("foo") }
-  override { io.write("foo") }
+  methodOnFoo { IO.write("foo") }
+  method(a) { IO.write("foo") }
+  method(a, b, c) { IO.write("foo") }
+  override { IO.write("foo") }
 }
 
 class Bar is Foo {
-  methodOnBar { io.write("bar") }
-  method(a, b) { io.write("bar") }
-  method(a, b, c, d) { io.write("bar") }
-  override { io.write("bar") }
+  methodOnBar { IO.write("bar") }
+  method(a, b) { IO.write("bar") }
+  method(a, b, c, d) { IO.write("bar") }
+  override { IO.write("bar") }
 }
 
 var bar = new Bar

test/inheritance/inherit_static_methods.wren

@@ -1,15 +1,15 @@
 class Foo {
-  static methodOnFoo { io.write("foo") }
-  static method(a) { io.write("foo") }
-  static method(a, b, c) { io.write("foo") }
-  static override { io.write("foo") }
+  static methodOnFoo { IO.write("foo") }
+  static method(a) { IO.write("foo") }
+  static method(a, b, c) { IO.write("foo") }
+  static override { IO.write("foo") }
 }
 
 class Bar is Foo {
-  static methodOnBar { io.write("bar") }
-  static method(a, b) { io.write("bar") }
-  static method(a, b, c, d) { io.write("bar") }
-  static override { io.write("bar") }
+  static methodOnBar { IO.write("bar") }
+  static method(a, b) { IO.write("bar") }
+  static method(a, b, c, d) { IO.write("bar") }
+  static override { IO.write("bar") }
 }
 
 Bar.methodOnFoo // expect: foo

test/inheritance/is.wren

@@ -5,12 +5,12 @@ var a = new A
 var b = new B
 var c = new C
 
-io.write(a is A) // expect: true
-io.write(a is B) // expect: false
-io.write(a is C) // expect: false
-io.write(b is A) // expect: true
-io.write(b is B) // expect: true
-io.write(b is C) // expect: false
-io.write(c is A) // expect: true
-io.write(c is B) // expect: true
-io.write(c is C) // expect: true
+IO.write(a is A) // expect: true
+IO.write(a is B) // expect: false
+IO.write(a is C) // expect: false
+IO.write(b is A) // expect: true
+IO.write(b is B) // expect: true
+IO.write(b is C) // expect: false
+IO.write(c is A) // expect: true
+IO.write(c is B) // expect: true
+IO.write(c is C) // expect: true