Now able to reap the rewards: since all that convoluted and tangled
old ''state tracking'' has been resolved and replaced by dedicated
and self-contained diagnostic subclasses, the old dummy BufferProvider
implementation can be detached, using a similar yet very simple
fake implementation.
For context: the `HeapMemBufferStore` is part of the default configuration
and thus automatically used whenever a unit test needs a `BufferProvider`.
This default implementation is not optimised for speed, and actually
never releases any memory, which allows to verify proper handling
of buffer memory allocation.