Parallel compact block downloads, take 3
Summary:
This PR attempts to mitigate a single case, where high bandwidth peers can bail us out of a flakey peer not completing blocks for us. We allow up to 2 additional getblocktxns requests per unique block. This would hopefully allow the chance for an honest high bandwidth peer to hand us the transactions even if the first in flight peer stalls out.
Backport of core#27626 and core#27743 (bugfix).
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Subscribers: PiRK
Differential Revision: https://reviews.bitcoinabc.org/D17082