...and as expected, this turns up quite some inconsistencies,
especially regarding usage of the »buffer types«.
Basically, the `PortBuilder` is responsible for the high-level functionality
and thus must ensure the nested `WiringBuilder` is addressed and parameterised
properly to connect all »slots« of the processing function.
- can use a helper function in the WiringBuilder to fill in connections
- but the actual buffer types passed over these connectinos are totally
unchecked at that level, and can not see yet how this danger can be
mitigated one level above, where the PortBuilder is used.
- it is still unclear what a »buffer type« actually means; it could
be the pointer type, but it could also imply a class or struct type
to be emplaced into the buffer, which is a special extension to the
`BufferProvider` protocol, yet seems to be used here rather to transport
specific data types required by the actual media handling library (e.g. FFmpeg)
* decision how to provide a default service for tests
while also allow for configuration of more specific services
* as starting point for the prototype: use the `TrackingHeapBlockProvider`
(simply because this is the only implementation available and tested)
Prototyping and analysis revealed that some aspects of the render node wiring
refers to effectively global services and can thus be taken out of the picture
by relying on classical ''Dependency Injection''
Consequently, `EngineCtx` needs a default implementation, which brings up
a simplistic fall-back version of those services in support for prototyping.
Moreover, dedicated lifecycle functionality must be provided to bring up
and shut down the actual service instances intended for operational use.
