don't require optional fields importing slashing protection information

[tersec]

#4149 changed this, but it's unclear why.

Meanwhile, since then:

$ build/nimbus_beacon_node slashingdb import ~/eip3076_example.json
Traceback (most recent call last, using override)
nimbus-eth2/vendor/nim-libp2p/libp2p/stream/bufferstream.nim(507) main
nimbus-eth2/vendor/nim-libp2p/libp2p/stream/bufferstream.nim(500) NimMain
nimbus-eth2/beacon_chain/nimbus_beacon_node.nim(2149) main
nimbus-eth2/beacon_chain/nimbus_beacon_node.nim(2002) handleStartUpCmd
nimbus-eth2/beacon_chain/nimbus_beacon_node.nim(1989) doSlashingInterchange
nimbus-eth2/beacon_chain/nimbus_beacon_node.nim(1962) doSlashingImport
Json load issue for file "eip3076_example.json"
eip3076_example.json(16, -7) Not all required fields were specified when reading 'SPDIR_SignedBlock'

using from https://eips.ethereum.org/EIPS/eip-3076#example-json-instance

{
  "metadata": {
    "interchange_format_version": "5",
    "genesis_validators_root": "0x4b363db94e286120d76eb905340fdd4e54bfe9f06bf33ff6cf5ad27f511bfe95"
  },
  "data": [
    {
      "pubkey": "0xb845089a1457f811bfc000588fbb4e713669be8ce060ea6be3c6ece09afc3794106c91ca73acda5e5457122d58723bed",
      "signed_blocks": [
        {
          "slot": "81952",
          "signing_root": "0x4ff6f743a43f3b4f95350831aeaf0a122a1a392922c45d804280284a69eb850b"
        },
        {
          "slot": "81951"
        }
      ],
      "signed_attestations": [
        {
          "source_epoch": "2290",
          "target_epoch": "3007",
          "signing_root": "0x587d6a4f59a58fe24f406e0502413e77fe1babddee641fda30034ed37ecc884d"
        },
        {
          "source_epoch": "2290",
          "target_epoch": "3008"
        }
      ]
    }
  ]
}

(genesis_validators_root modified for mainnet compatibility for easier testing)

With this PR's change:

$ build/nimbus_beacon_node slashingdb import ~/eip3076_example.json
INF 2023-05-26 21:30:34.479+00:00 No slashing protection data for validator - initiating topics="antislash" validator=b845089a1457f811bfc000588fbb4e713669be8ce060ea6be3c6ece09afc3794106c91ca73acda5e5457122d58723bed
Import finished: 'eip3076_example.json' into '.cache/nimbus/BeaconNode/validators/slashing_protection.sqlite3'

https://eips.ethereum.org/EIPS/eip-3076#json-schema confirms that these signing_root fields are, in fact, optional and not required.

https://github.com/status-im/nimbus-eth2/blob/unstable/tests/slashing_protection/test_fixtures.nim and https://github.com/status-im/nimbus-eth2/blob/unstable/tests/slashing_protection/test_slashing_protection_db.nim test that these schema variations work, but in this case, nimbus_beacon_node has been preventing the slashing protection database import code from ever seeing the JSON.

[github-actions]

Unit Test Results

         9 files  ±0    1 071 suites  ±0   34m 23s ⏱️ - 1m 0s
  3 701 tests ±0    3 420 ✔️ ±0  281 💤 ±0  0 ❌ ±0 
15 772 runs  ±0  15 458 ✔️ ±0  314 💤 ±0  0 ❌ ±0 

Results for commit 31719d4. ± Comparison against base commit 750722d.

♻️ This comment has been updated with latest results.

[zah]

Since requireAllFields honors the optionality of fields using the Option[T] type, another fix is to explicitly mark the optional fields as such. requireAllFields = false is a more dangerous policy that may allow genuinely invalid SPDIR files to be processed. Please note that I haven't looked at the specifics of the SPDIR format before making this comment - I assume that not all fields are optional.

[tersec]

Since requireAllFields honors the optionality of fields using the Option[T] type, another fix is to explicitly mark the optional fields as such. requireAllFields = false is a more dangerous policy that may allow genuinely invalid SPDIR files to be processed. Please note that I haven't looked at the specifics of the SPDIR format before making this comment - I assume that not all fields are optional.

31719d4

Indeed, this marks only optional fields as optional.

The specific stand-in value of 0x0 was what, in practice, it already used when the signing_root field was missing, so this doesn't change the semantics of that case.