This PR fixes an issue that when peers legitimately lack a requested
BAL, empty (0x80) is delivered and this BAL entry will be refetched
over and over again.
A `refused` tracker is added and catchUp will fail if this BAL is
unavailable against the entire peerset.
Adds snap/2 (EIP-8189), a block-access-list (BAL) based state sync, and
wires it to run side by side with snap/1. It's opt-in (for now) behind a
new --snap.v2 flag and chosen at startup.
https://eips.ethereum.org/EIPS/eip-8189
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Co-authored-by: Toni Wahrstätter <info@toniwahrstaetter.com>
Co-authored-by: Gary Rong <garyrong0905@gmail.com>
This PR is a prerequisite for landing snap v2, the BAL-healing snap sync
algorithm.
It duplicates much of the snap v1 skeleton, which is expected to be
deprecated once v2 is enabled. The code duplication is acceptable as a
short-term tradeoff, simplifying development and reducing integration
complexity.
