core[patch]: Require explicit override for callbacks within a nested config

[jacoblee93]

Something like this seems like it should trace properly:

const lambda = RunnableLambda.from(async (input: string) => {
  const nestedLambda = RunnableLambda.from(
    async (input: string) => input);
  );
  const newConfig = {
    runId: "foo",
  }
  return nestedLambda.invoke(input, newConfig);
});

But it currently does not since newConfig will override existing callbacks, even though that is unlikely to be the user's intention.

This PR will load in any nested callbacks by default unless the passed config explicitly removes them.

CC @nfcampos

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