jscore: Add parseAccountKey, Fix parseTransaction and parseTxType

[blukat29]

• Add parseAccountKey(rlp) -> object

• AccountKeyWeightedMultiSig now accepts both representations:

  // array-of-objects: Recommended format
  {
    type: 4,
    threshold: 2,
    keys: [
      { weight: 1, key: "0x02c734b50ddb229be5e929fc4aa8080ae8240a802d23d3290e5e6156ce029b110e" },
      { weight: 1, key: "0x0212d45f1cc56fbd6cd8fc877ab63b5092ac77db907a8a42c41dad3e98d7c64dfb" },
    ]
  }

  // array-of-tuples: Supported for backward compatibility
  {
    type: 4,
    threshold: 2,
    keys: [
      [1, "0x02c734b50ddb229be5e929fc4aa8080ae8240a802d23d3290e5e6156ce029b110e"],
      [1, "0x0212d45f1cc56fbd6cd8fc877ab63b5092ac77db907a8a42c41dad3e98d7c64dfb"],
    ]
  }

• Fix parseTransaction to return numeric fields in proper format

  • not 0x but 0x0
  • not BigNumber but hex strings

• Fix parseTxType to accept bigint and null types