[wip] Stripe downloads to reduce stallers occuring #9338

Mitigates #9213

This may also help reduce the unresponsiveness of peers during IBD as often they encounter a big chunk of contiguous blocks that need to be added to the chain due to the current contiguous way they are downloaded.

This is WIP... also need to make it so that it doesn't download the inbetween blocks from the same peer before a new peer has a chance.

Can you work on your own project and submit PR once ready?

I do not know how it looks like for others, but for me, it is a bit more than I can absorb.

@paveljanik It's ready for testing now. I am currently doing further testing, and will post results shortly. It was ready when I raised the PR, but is more ready now. I didn't raise the PR prematurely as the functionality was still an improvement over what was already there.

@paveljanik I'd like to have a conversation with you to better understand what you are meaning regarding absorption, but here is probably not the place - where might be? Telegram perhaps? https://telegram.me/rebroad

Ok, on 2nd thoughts I might have been overly enthusiastic raising this PR, as I realise that it won't work well in some situations, e.g. when connecting to too few peers but I do think that the advantage of github is the collaboration, and therefore it can be more efficient to advertise work in progress as several heads can sometimes find solutions sooner than one. At least, this is how I understand the process working.

Anyway, from some perspectives I may have jumped the gun. Should I close this until it's more developed then?

There's a fault in the logic here, which I have fixed and am testing and will push once tested.

not ready - needs bandwidth per node measuring before it provides real benefits.