feat: implement config option 'finalize' to specify when to stop processing blocks

[jmhrpr]

This implements a finalize configuration option similar to in Oura. You can use it to make Scrolls stop processing blocks after processing a block with a specified hash or the first block which was created on or after a specified absolute slot.

For example you would include the following in your config to stop processing new blocks after processing the block with hash fafd996ddd3d2fdb2bf2a5dd5a3b32d0827fc53634871c85c5441959d7dae795:

    "finalize": {
        "until_hash": "fafd996ddd3d2fdb2bf2a5dd5a3b32d0827fc53634871c85c5441959d7dae795"
    },

Or to stop processing new blocks after processing the first block which was created on or after slot 1713945:

    "finalize": {
        "max_block_slot": 1713945
    },

Tested with N2N.