[Cin] Some tests on blending

In reference to the email: https://www.mail-archive.com/[email protected]/msg04905.html and to the whole of the following discussion, which includes a workaround by IgorBeg. I have tried further testing, now that we have Blend Algebra that allows us to customize the various Blends. I do not know whether it is appropriate to reopen an issue that is now closed and has also led to tensions (you can see the article: https://linuxvideoediting.blogspot.com/2022/09/transparent-text-effect-with-.... I warn that it contains polemics). So I will only report the result of some of my tests; they are probably not even worth reading.