Potential to modify ordering for IS_TEST in lib module

[Chines Wang]

ureq/src/lib.rs

Lines 479 to 485 in 4e3169f

 pub fn is_test(is: bool) -> bool { 
     static IS_TEST: Lazy<AtomicBool> = Lazy::new(|| AtomicBool::new(false)); 
     if is { 
         IS_TEST.store(true, Ordering::SeqCst); 
     } 
     IS_TEST.load(Ordering::SeqCst) 
 } 

SeqCst is overly restrictive. I believe that the ordering can be appropriately modified.

In lib model, I believe that IS_TEST is merely signals for multithreading purposes and do not synchronize with other locals. Therefore, using Relaxed ordering should suffice.

(happy to make a PR if this looks reasonable)

[Martin Algesten]

Sure PR is good. Doesn't make any difference really since this is not a very used code path.