Require flag when resuming from past-weak-subjectivity database / genesis

[arnetheduck]

This proposal introduces a new flag, --long-range-sync, that takes effect whenever the most recent state in the database (or genesis, if no database) is older than the weak subjectivity period and no trusted pivot point is given:

• --long-range-sync=light, default - light client protocol is required to verify the long-range sync (https://github.com/metacraft-labs/DendrETH/tree/main/docs/long-range-syncing)
  • client shuts down otherwise with a message suggesting TNS or lenient
• --long-range-sync=lenient - allows forward-syncing beyond WSP, including syncing from genesis