ledger stream onMessage: returns different type than expected

[acharb]

Describe the bug

When streaming ledgers with typescript the sdk says to expect CollectionPage<LedgerRecord>, however the value received is just the ledger record

Makes it so have to type assert to LedgeRecord in order to use the value properly

What version are you on?

@stellar/stellar-sdk@^12.0.0-rc.2"

To Reproduce

import { Horizon } from "@stellar/stellar-sdk";

const streamTest = async () => {
  const horizon = new Horizon.Server("https://horizon-testnet.stellar.org");
  horizon
    .ledgers()
    .cursor("now")
    .limit(200)
    .stream({
      onmessage: async (
        msg: Horizon.ServerApi.CollectionPage<Horizon.ServerApi.LedgerRecord>,
      ) => {
        console.log(msg.closed_at); // throws error that .closed_at does not exist
      },
    });
};

streamTest();

In order to resolve have to do:

const streamTest = async () => {
  const horizon = new Horizon.Server("https://horizon-testnet.stellar.org");
  horizon
    .ledgers()
    .cursor("now")
    .limit(200)
    .stream({
      onmessage: async (msg: any) => {
        console.log((msg as Horizon.ServerApi.LedgerRecord).closed_at);
      },
    });
};

streamTest();

Trying to declare the param as LedgerRecord like so:

msg: Horizon.ServerApi.LedgerRecord

throws an error at compile time

Expected behavior

The onMessage value type should be LedgerRecord