fix: use Set over the Array instance for paused hostnames

[smalluban]

Fixes #1651

Still, I am not sure if this is better. The real question is if Array.prototype.includes is much slower than Set.prototype.has... The list has unique IDs (so no benefit here), and it must be cleared each time, as otherwise, we would need to check if the user removed the domain (and it might be then even slower).

[philipp-classen]

The back-and-forth converting could be avoided, I assume, but modeling the underlying data structure:

paused = [{ id: "foo", ...rest1 }, { id: "bar", ...rest2 }, ...]

as

paused = {
  foo: { ...rest1 },
  bar: { ...rest2 },
  ...
}

But I'm also fine with keeping the array structure if it is difficult to change.

[smalluban]

The dynamic keys are not supported in Store.