Handle ByteBufferAllocator gracefully

We have introduced the interface ByteBufferAllocator a while ago. This interface has its release method while parquet-mr does not test it whether it is invoked properly in all required situations.
We need to add tests for this and fix the potential issues.

Note: In most cases the release method is a no-op so not invoking it would not cause any issues. Meanwhile, if someone would implement their own ByteBufferAllocator that requires the release method to be invoked we might generate memory leaks failing to do so.