Integration Tests for BatchReceiveAsync

[Ttpetrov]

Environment used .Net 8.0 C#/Pulsar Server4.0.0

Summary: Added two new integration tests for batch receive functionality to verify correct behavior with message backlogs.
Tests Added:

1. "Batch receive respects max size with large backlog" ✅
   • Verifies that BatchReceiveAsync() respects the configured maxBatchSize (8 messages) when consuming from a large pre-existing backlog (2000 messages)
   • Produces all messages BEFORE consumer subscription to ensure backlog exists
   • Validates that no batch exceeds the configured maximum size
2. "Batch receive respects max size with large backlog and concurrent production" ❌ (Expected to Fail)
   • This test is currently failing and is EXPECTED to fail
   • Demonstrates a potential bug/limitation where batch size limits are violated when:
   • A large backlog exists (2000 messages)
   • Additional messages are continuously produced during consumption (1000 more messages)
   • Consumer has simulated processing delays (500ms per batch)
   • The failure reveals that concurrent production + backlog may cause BatchReceiveAsync() to return batches larger than the configured maxBatchSize
   Purpose: The second test documents the reproduction case for investigation and future fix. It should remain as a failing test until the underlying issue is resolved.

[Lanayx]

Thank you for an example of the failing test! I was able to locate the problem and cover it with much simpler unit tests here