Fix race condition in ChannelCoordinator startup: wait for receiver readiness before reading localMember

[ABin-Huang]

Problem

ChannelCoordinator.internalStart() calls clusterReceiver.start() and then immediately calls getChannel().getLocalMember(false) without waiting for the receiver's background thread to enter the listen loop. This creates a race window where:

1. The NioReceiver listener thread may not have executed setListen(true) yet
2. The membershipService may not have initialized localMember
3. The local member's host/port properties may be unset or default values

This can cause intermittent cluster communication failures where nodes cannot connect to each other because the advertised host/port is incorrect.

The original code had a // synchronize, big time FIXME comment at this location.

Fix

Added a readiness signaling mechanism based on CountDownLatch:

1. ChannelReceiver interface: Added waitForReady(long timeout, TimeUnit unit) default method that returns true immediately (backward compatible). Added DEFAULT_READY_TIMEOUT_MS constant.

2. NioReceiver: Added volatile CountDownLatch readyLatch. A fresh latch with count=1 is created in start() before launching the listener thread. The latch is counted down in listen() after setListen(true). waitForReady() is overridden to await the latch. Latch is reset to count=0 in stopListening() to support restarts.

3. ChannelCoordinator: After clusterReceiver.start(), calls waitForReady(5000ms) before reading getLocalMember(). Throws ChannelException on timeout or interruption. Removed the FIXME comment.

Testing

Added TestChannelCoordinatorStartupRace with 5 test cases:

1. testWaitForReadyDefaultMethodReturnsImmediately - Verifies backward compatibility of the default method
2. testNioReceiverReadyLatchContract - Verifies CountDownLatch lifecycle via reflection
3. testChannelCoordinatorWaitsForReceiverBeforeLocalMember - Verifies exact call order: start() → waitForReady() → getLocalMember() → setLocalMemberProperties()
4. testChannelCoordinatorThrowsWhenReceiverNotReady - Verifies ChannelException on timeout and that getLocalMember is NOT called
5. testChannelCoordinatorHandlesInterruptedException - Verifies interrupt status is restored and ChannelException is thrown

Files Changed

• java/org/apache/catalina/tribes/ChannelReceiver.java - Add waitForReady() default method
• java/org/apache/catalina/tribes/transport/nio/NioReceiver.java - Add CountDownLatch readiness signaling
• java/org/apache/catalina/tribes/group/ChannelCoordinator.java - Wait for receiver readiness before reading localMember
• java/org/apache/catalina/tribes/group/LocalStrings.properties - Add new i18n messages
• test/org/apache/catalina/tribes/group/TestChannelCoordinatorStartupRace.java - Add unit tests

Note: This PR supersedes #1061 and #1060. The branch is based on the latest main (fork synced to 719edeaa).