Add stress test and fix race it detected

pool.go

@@ -285,7 +285,9 @@ func (p *Pool) Acquire(ctx context.Context) (*Resource, error) {
 
 			select {
 			case <-ctx.Done():
+				p.cond.L.Lock()
 				p.canceledAcquireCount += 1
+				p.cond.L.Unlock()
 
 				// Allow goroutine waiting for signal to exit. Re-signal since we couldn't
 				// do anything with it. Another goroutine might be waiting.