Make the `TransactionResponse.waitForResult` method private about fuels-ts

[nedsalk]

I don't know the internals fully, but to me it feels a bit off to actually even have .wait() and .fetch() method on a TransactionResponse class. Shouldn't a *Response class be the result of some fetching that happened somewhere else and not it be the one fetching? We should maybe rethink the naming or, if the naming is actually correct, add some documentation on why this specific naming is correct, as it's counterintuitive at first glance.

[Dhaiwat10]

@nedsalk I think it is because the promise returned by .call() is resolved once the transaction is successfully sent to the chain. The transaction needs to be mined and confirmed next, and this takes a while. The promise returned by .wait() is resolved when the transaction is finalized/confirmed.