remove a race from the hashing write()

Calling load() and store() separately leaves a lot of opportunity for a
race to occur.

This changes the logic to use compare_exchange() and will only return if
the previous value is absolutely not 1 at the point of comparison.

I also don't think this needs to be SeqCst, so relaxing that requirement
a little.

src/config/hashing.rs

@@ -50,9 +50,11 @@ impl HokmaLock {
 
     pub fn write(&'static self) -> WhenTheHokmaSuppression {
         loop {
-            let previous = self.lock.load(Ordering::SeqCst);
-            self.lock.store(1, Ordering::SeqCst);
-
+            // We are only interested in error results
+            if let Err(previous) = self
+                .lock
+                .compare_exchange(1, 1, Ordering::Acquire, Ordering::Relaxed)
+            {
                 if previous != 1 {
                     return WhenTheHokmaSuppression {
                         hokma: self,
@@ -62,6 +64,7 @@ impl HokmaLock {
             }
         }
     }
+}
 
 struct WhenTheHokmaSuppression {
     hokma: &'static HokmaLock,