erigon snapshot preverified provenance and block height

From https://discord.com/channels/687972960811745322/886550095749873666/1450936809369632908:

> I'm thinking it'd be useful if there were a subcommand (probably of erigon snapshots) that would print either/both of:
> the resolved effective source (R2 URL, github URL) for preverified.toml (i.e. what would get used if erigon snapshots reset were run)
> the block height up to which said current resolved remote preverified.toml covers, when fetched+parsed
> (it'd also be useful if erigon would log either / both of these during OtterSync stage)

Start by tracing the erigon snapshots reset subcommand and the OtterSync stage, focusing on how preverified.toml is resolved, fetched, and parsed. Done means the relevant command or stage reports the effective source URL and the covered block height, with behavior confirmed by the project's existing tests.

Written by the indexing model from the issue text.