Add retry mechanism when downloading genesis and snapshots

[mvines]

When the validator selects an RPC node to download genesis or a snapshot from, it currently aborts the process on any failure. This is ripe for exploitation (as we saw in the SLP2 boot) and can cause problems such as #8406 when the selected RPC node returns bad data.

While this PR does not add any additional genesis/snapshot validation (that's for a follow-up), it adds the ability to blacklist any RPC nodes that fail to respond or return unexpected results. Caveats:

• --trusted-validator nodes are never blacklisted
• Once all visible nodes are blacklisted, if no new nodes appear in 60 seconds then the blacklist is cleared and all nodes will be retried again.

Progress towards #8406

[codecov]

Codecov Report

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The diff coverage is 33.3%.

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[mvines]

Obsoleted by #8474