[Tests] Fix OutOfMemoryError and NoClassDefFoundErrors in tests #15911
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Fixes #15689
Fixes #15793
Fixes #15897
Motivation
PulsarByteBufAllocator.DEFAULTinstance was replaced in BatchMessageContainerImplTest, but never restored. This caused strange issues in many unit tests. OutOfMemoryError and NoClassDefFoundErrors were most likely caused by the BatchMessageContainerImplTest.Modifications
Fix the problems in BatchMessageContainerImplTest and reset the state after the test completes.
Additional context
The flaky test was introduced by #12170 which has been cherry-picked to branch-2.8, branch-2.9 and included also in branch-2.10 .