Fix concurrent subscription consumer handshakes

[Caideyipi]

What is changed

• Serialize handshakes for the same subscription consumer identity and atomically transfer ownership to the newer connection.
• Fence the replaced receiver with status 1919 so stale heartbeats, subscriptions, and handshakes cannot affect the active consumer.
• Treat consumer fencing as a terminal client state: stop background workers and reconnect attempts, close only the transport session, and preserve the dedicated exception.
• Add English/Chinese messages and regression tests for concurrent handshakes, late handshakes/exits, client lifecycle, and poll handling.

Verification

• mvn test-compile -DskipTests
• mvn test-compile -P with-zh-locale -DskipTests
• client subscription regression tests: 10 passed
• datanode subscription receiver regression tests: 24 passed