core: add debug line when an IO backend is created. A user can check that the correct one has been selected.

core/io/windows.rs

@@ -1,5 +1,5 @@
 use crate::{Completion, File, LimboError, OpenFlags, Result, IO};
-use log::trace;
+use log::{debug, trace};
 use std::cell::RefCell;
 use std::io::{Read, Seek, Write};
 use std::rc::Rc;
@@ -8,6 +8,7 @@ pub struct WindowsIO {}
 
 impl WindowsIO {
     pub fn new() -> Result<Self> {
+        debug!("Using IO backend 'syscall'");
         Ok(Self {})
     }
 }