During the last days, I started with analysis to find a way
to operate the `BufferProvider`, as implemented thus far,
within a massively concurrent environment.
Since I intend to create thread-local caches,
the initialisation of the `BufferMetadata` store must be static.
It turns out that the root-ID, which acts like a mandator ID,
is only used at a single code path, when creating or accessing
an abstract type-Key. It is thus easy to extract and relocate
this distinguishing ID into the actual `BufferStage` implementation.