Panic on closed channel

[sfleiter]

I had a look on #15 since I was "lucky" and can reproduce this more than 95% of runs.

I had to restructure the code quite a bit but avoided to change any behavior.
Please report if you see anything.
For me this runs now successfully every time.

Most important part is to not close any channel.
In go you only have to close channels if you want to use that as a mechanism to tell the receiver no more values are coming, see f.e. https://go.dev/tour/concurrency/4

For everything else please look through the individual commits, that will probably be easier to understand the refactoring.

[tg44]

I think this is smart, only one question below;