Pipe: Fix NullPointerException in concurrent event access

[luoluoyuyu]

Description

Fix NullPointerException caused by concurrent access to insertNode field in pipe transfer.

Root Cause:

1. TOCTOU race condition: insertNode field accessed multiple times without synchronization
2. Reference counting gap: In batch mode, getDeviceId() called before reference count increased

Changes:

1. Use local variable snapshots in PipeInsertNodeTabletInsertionEvent to avoid repeated mutable field access
2. Protect event access with reference counting in PipeTransferBatchReqBuilder
3. Add reference counting protection in WebSocketSink for toRawTabletInsertionEvents() call

Fixed methods in PipeInsertNodeTabletInsertionEvent:

• getDeviceId(): double layer protection (node + targetPath snapshot)
• getByteBuffer(): added null check
• isGeneratedByPipe(), throwIfNoPrivilege(), toString(), coreReportMessage(), ramBytesUsed()

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This PR has:

• been self-reviewed.
  • concurrent read
  • concurrent write
  • concurrent read and write
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods.
• added or updated version, license, or notice information
• added comments explaining the "why" and the intent of the code wherever would not be obvious
  for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold
  for code coverage.
• added integration tests.
• been tested in a test IoTDB cluster.

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Key changed/added classes (or packages if there are too many classes) in this PR

[Caideyipi]

Better remove the stack printed at "ignored because the failure event is released", just use e.getMessage() or null if e == null

[Caideyipi]

LGTM