ZOOKEEPER-4947: Close clients after authentication failure

[1fanwang]

A client that fails SASL authentication stays in AUTH_FAILED when the caller closes it. The close guard treats every non-alive state as already closed, so it skips the connection shutdown and leaves the client threads running.

This narrows the early return to CLOSED. Authentication failures now use the normal disconnect path, while repeated close calls remain idempotent.

Related:

• https://issues.apache.org/jira/browse/ZOOKEEPER-4947
• https://issues.apache.org/jira/browse/ZOOKEEPER-4948

Testing

$ SOURCE=zookeeper-server/src/main/java/org/apache/zookeeper/ZooKeeper.java
$ git checkout 7af463e0fd -- "$SOURCE"
$ JAVA_HOME=$(/usr/libexec/java_home -v 21) mvn -pl zookeeper-server -am test \
    '-Dtest=SaslAuthFailTest#testBadSaslAuthNotifiesWatch' \
    -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false
expected: <CLOSED> but was: <AUTH_FAILED>
Tests run: 1, Failures: 1, Errors: 0, Skipped: 0

$ git checkout 5a201d633f -- "$SOURCE"
$ JAVA_HOME=$(/usr/libexec/java_home -v 21) mvn -pl zookeeper-server -am test \
    -Dtest=SaslAuthFailTest \
    -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS