v2: Cooler

[PierreMardon]

For v2 I want to implement an overall alignment on KotlinRetrier.
Indeed, after using both a lot, I came to the conclusion that implementing a hot flow is less convenient - and by a lot.

What I want is to create simple structs like current ColdRetrier that would also hold the job, and be themselves publishers.
Having two subscriptions would mean executing two retrier publishers.

It implies a rewriting that should simplify the code, because the shared behavior was a huge constraint, and it was probably not implemented very simply.