@Override
    public Object getAttachments() {
        return attachments;
    }
A helper future for bool result failover, which is an immutable object.
A new object will be created when a retry operation occurs and
{@code retriesLeft} will decrease by 1, until {@code retriesLeft} == 0.

@author jiachun.fjc
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/client/failover/impl/BoolFailoverFuture.java