...to the base-class of all tests
* `seedRand()` shall be invoked by every test using randomisation
* it will draw a new seed for the implicit default-PRNG
* it will document this seed value
* but when a seed was given via cmdline, it will inject that instead
* `makeRandGen()` will create a new dedicated generator instance,
attached (by seeding) to the current default-PRNG
It is not clear yet how to pass the actual `SeedNucleus`, which
for obvious reasons must be maintained by the `test::Suite`
This is the first step towards a »Test Domain Ongology« #1372,
which is a systematic arrangement of test-dummy functionality assumed
to mirror the actual media processing functionality present in external libs.
Each media-processing library not only provides functions to crunch data,
but also establishes a framework of entities and classification to determine
what »media« is an how it is structured and can be generated, transformed
and qualified. Since a essential goal for Lumiera is to be **library agnostic,**
it is important to avoid naïvely to take some popular library's choices
as universal truth regarding structure and nature of »media« as such.
Rather, the architecture of the Lumiera Render Engine must be kept
sufficiently open to accommodate the working style of various libraries,
even ones not known today.
To validate this architectural openness, we use a set of test functions
unrelated to any existing library to validate access to and usage of
rendering functionality — followed by further steps to adopt existing
popular libraries like **FFmpeg** or **Gstreamer**, without tilting
the basic structure of the Render Engine one way or the other.
