Make Effect.publisher eager

[mbrandonw]

Makes the trailing closure of Effect.publisher { … } non-escaping, and hence the publisher is created eagerly when the effect is constructed. This means you can access state inside the closure, which will be handy in the shared state tools coming to TCA soon:

return .publisher { 
  state.$shared.publisher
    .map(Action.sharedUpdated)
}

Note, however, the publisher is not run eagerly. That is still delayed until state changes have been processed and all effects are started together.

We don't think there is a big use case for needing the construction of a publisher to be lazy since the publisher itself can encapsulate lazy work, but if for whatever reason one needs to lazily create the publisher then you can use Deferred:

return .publisher {
  Deferred {
    // create publisher
  }
}

[stephencelis]

Seems like a general improvement! Let's just be careful to mention the change in the logs for folks that may be impacted by the change.