feat: rename IO.write to IO.print and add Unicode escape support in strings

Rename the IO.write method to IO.print, which now prints without a trailing newline, and add a new IO.print method that appends a newline after output. Update all benchmark, example, and test files to use IO.print instead of IO.write. Additionally, implement Unicode escape sequence parsing in the compiler's string tokenizer, supporting \uXXXX and \u{...} syntax with proper UTF-8 encoding for code points up to U+10FFFF.

test/io/write.wren

@@ -3,10 +3,10 @@ class Foo {
 }
 
 // Calls toString on argument.
-IO.write(new Foo) // expect: Foo.toString
+IO.print(new Foo) // expect: Foo.toString
 
 // Returns argument.
-var result = IO.write(123) // expect: 123
-IO.write(result == 123) // expect: true
+var result = IO.print(123) // expect: 123
+IO.print(result == 123) // expect: true
 
 // TODO: What if toString on argument doesn't return a string?