chore: cleanup to metadata and extrinsic effect apis

[harrysolovay]

Now that various effects utilize Z.Name, we can attach methods to simplify their APIs.

Metadata:

const entryMetadata = new C.Metadata(T.polkadot)
  .pallet("Balances")
  .entry("Account");

Extrinsics:

const root = new C.Extrinsic(T.westend, {
  sender: {
    type: "Id",
    value: T.alice.publicKey,
  },
  palletName: "Balances",
  methodName: "transfer",
  args: {
    value: 12345n,
    dest: {
      type: "Id",
      value: T.bob.publicKey,
    },
  },
})
  .signed((message) => ({
    type: "Sr25519",
    value: T.alice.sign(message),
  }))
  .watch((stop) => {
    return (event) => {
      // ...
    };
  });

^ this paves the way for the non-watched counterpart.