fix: do not show warnings when workers >= 10

[simoneb]

Replaces ora with char-spinner to avoid the warning altogether.

old explanation

I didn't actually figure out the root cause of why this is happening, and I do realize that making this initialization eager is doing something that's probably unnecessary unless workers are being used. Nevertheless, that's the most reliable way I found to fix this.

The problem seems to come from the bl package used by ora, which does some fancy stream manipulation, eventually leading to the warnings being generated.

Making the initialization of ora eager in the module root makes the issue disappear.

Closes #337

[simoneb]

even if I move the instantiation here, it will still cause the test failure. moving it outside this method is what fixes it

[salmanm]

I think the problem starts when Ora tries to mute process.stdout stream. And process.stdout._events.xxx already contains n (number of active workers) listeners (gets added right after the call to new Worker).
So I appreciate that it's not straightforward.

But why don't we simply get rid of Ora!? I know it's widely used but if it's causing problems, I think it's worth looking for alternatives. char-spinner for instance, it's very old and not actively maintained, but I think it works fine and a very simply code base. I'd say we start using it, and if we need to tweak, we can just fork it.

[simoneb]

@salmanm fair point. I changed the implementation. rationale was, I'd spent quite some time looking into the issue and the solution seemed good enough. char-spinner is much simpler it turns out so it's a more robust solution indeed. I'd assumed there was some thought put into choosing the spinner library so I didn't consider reverting that decision

[mcollina]

lgtm