fix: migrate to snapshot.js 0.8-beta with ofetch support

[wa0x6e]

Following #702, which was reverted for safety, but found out later that the revert reason was unrelated to the PR.

This PR:

• update the snapshot.js SDK to 0.8-betam with ofetch support
• refactor the vp operation to handle the new error handling (getVp now always return a JSON-RPC error)
• Throw a more structured error when failing to get Vp

Before the update, error looks like:

{
  "errors": [
    {
      "message": "Unexpected error value: { code: 500, message: \"unauthorized\", data: { reason: null, code: \"CALL_EXCEPTION\", method: \"aggregate((address,bytes)[])\", data: \"0x\", errorArgs: null, errorName: null, errorSignature: null, address: \"0xcA11bde05977b3631167028862bE2a173976CA11\", args: [Array], transaction: [Object] } }",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "vp"
      ]
    }
  ],
  "data": {
    "vp": null
  }
}

After update, looks like:

{
  "errors": [
    {
      "message": "failed to get voting power",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "vp"
      ],
      "extensions": {
        "code": 500,
        "message": "unauthorized",
        "data": {
          "reason": null,
          "code": "CALL_EXCEPTION",
          "method": "aggregate((address,bytes)[])",
          "data": "0x",
          "errorArgs": null,
          "errorName": null,
          "errorSignature": null,
          "address": "0xcA11bde05977b3631167028862bE2a173976CA11",
          "args": [
            [
              [
                "0xc23f41519d7dfadf9eed53c00f08c06cd5cdde54",
                "0x70a08231000000000000000000000000be551154399b14c30a609d4517b5897a82bc7d47"
              ]
            ]
          ],
          "transaction": {
            "data": "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",
            "to": "0xcA11bde05977b3631167028862bE2a173976CA11"
          }
        }
      }
    }
  ],
  "data": {
    "vp": null
  }
}

Tested with following query (on testnet):

query Vp {
  vp(voter: "0xbe551154399b14c30A609D4517b5897a82BC7D47", 
    space: "karate-combat-stage-1.eth", 
    proposal: "0xac90046be202be13a689ea22dd38fbe1ac09731a0c5cdb85229bb0615ca2c10b") {
    vp
    vp_by_strategy
    vp_state
  }
}