Remove the neverAbortedSignal

[ghost91-]

This PR removes the neverAbortedSignal and instead simply does not pass a signal by default. The behavior is essentially the same, but it simplifies the code a bit, in my opinion.

Unfortunately, this is technically a breaking change because consumers might rely on always receiving a signal. So I'm not sure whether this is actually worth doing, but I wanted to bring it up nonetheless. For example, if a major release is planned anyways for other reasons, it might make sense to slip this in.

[connor4312]

I'm not a very big fan of this. I see that it's useful for consumers to save a little bit of work if they don't know whether an abort signal will get passed and can avoid adding listeners to the neverAbortedSignal, but this is a pretty marginal performance difference and makes other usability harder because now all code must check whether the signal is passed before they can use it.

[ghost91-]

Fair point. I'm very used to dealing with optional things by using optional chaining and typically, the signal is optional anyways where you pass it into (fetch, axios, etc.), so I didn't think of it as a big deal (aside from it being a breaking change).

To be honest, the performance improvement isn't even the main argument for me, it's that the code becomes a bit easier to understand, in my opinion. But maybe we disagree on that. Feel free to close this if you think we should not do it.