feat: decoding extrinsics within blocks

[harrysolovay]

import { polkadot } from "capi/known";

const result = await polkadot.block().read();

result.block.extrinsics may look––for example––as follows:

[
  {
    protocolVersion: 4,
    signature: undefined,
    palletName: "Timestamp",
    methodName: "set",
    args: { now: 1656730165771 }
  },
  {
    protocolVersion: 4,
    signature: undefined,
    palletName: "ParaInherent",
    methodName: "enter",
    args: {
      data: {
        bitfields: [Array],
        backed_candidates: [Array],
        disputes: [Array],
        parent_header: [Object]
      }
    }
  }
]