Retrieval checkForActiveDeal is too aggressive

[magik6k]

I'm not sure why exactly we want to stop duplicate retrievals for the same piece, but checkForActiveDeal should at least permit retrievals for the same piece with different selectors.

Being able to only do a single retrieval per piece in parallel severely limits tools like filecoin-project/lotus#9382.

[dirkmc]

Looks like it was implemented as a requirement of filecoin-project/lotus#5443

I agree though, there's not really a good reason to prevent multiple concurrent deals.

[hannahhoward]

honestly yall can do whatever you want. go-fil-markets retrieval client is ONLY used by Lotus. It should probably move directly into the Lotus repo.

everybody else uses FilClient.