refactor(backend): simplify address balance query

[ShookLyngs]

Changes

• Simplify the logic of querying satoshi and pendingSatoshi in the BitcoinAddress
• Resolves refactor: btcAddress.balance = funded_txo_sum - spent_txo_sum #10

Test

This is a random transaction I picked on the testnet of mempool.space:

GraphQL request:

{
  btcTransaction(txid: "b062e7a378e86731a8dae6f1940bd963c020ca4911bc4cb26256b5c77d529087") {
    vout {
      address {
        address
        satoshi
        pendingSatoshi
      }
    }
  }
}

Response:

{
  "data": {
    "btcTransaction": {
      "vout": [
        {
          "address": {
            "address": "tb1qc73j0up2l7rfahcj2g3yayccm9rjd5chr0uqyd",
            "satoshi": 11211,
            "pendingSatoshi": 5824
          }
        },
        {
          "address": {
            "address": "tb1qdaprd34l5kmvajgmpcakldu9a7dgtwmlkavh7v",
            "satoshi": 11602902,
            "pendingSatoshi": -6529
          }
        }
      ]
    }
  }
}

Screenshots:

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