RATIS-2630. Netty data-stream shutdown leaks in-flight streams

[spacemonkd]

What changes were proposed in this pull request?

RATIS-2630. Netty data-stream shutdown leaks in-flight streams

• On shutdown, DataStreamManagement.shutdown() only stopped the request/write executor pools.
• In-flight streams left in the streams map were never drained, leaking their local DataStream resources (open file channels) and remote outputs on stop/restart.
• Fixed by draining the map after the executors stop — reusing cleanUp(streams.keySet()) — and added StreamMap.keySet() to enumerate the remaining streams.
• Added a TestDataStreamManagement case asserting an in-flight (header-only, no CLOSE) stream is released and unregistered after shutdown().

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-2630

How was this patch tested?

Tested using unit tests