test: slot hash comparison scripts

- python scripts to diff agave and sig
    - download recent snapshot, run agave, shred network, create artifact containing minimized snapshot, agave ledger, sig ledger.
    - run sig and agave from artifact and diff slot hashes
- sig changes to support scripts:
    - custom validator directory
    - download genesis files
    - ledger bounds + purge
    - flag to print current root