Make Event sync between instances in distributed setups

[rodja]

Motivation

Currently it's tricky to appreciate the Event demo in the documentation: when sending a "tweet" it only appears on visitors of the same instance. Due to the distributed deployment via fly.io, if a user opens two tabs, they have a high chance of landing on different instances.

Implementation

This PR is currently just an (AI-aided) sketch of an idea I had after some research. By using Zenoh to transparently sync events across instances. Zenoh is great for this because it does not need a broker or seperate server (like MQTT or Redis). Instances simply auto-discorver. To test it, I created a new example called distributed: A docker swarm starts three NiceGUI instances and a Traefik proxy in front:

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
  • error handling, edge cases, ... there is still much much to do before it might be ready
• Pytests have been added.
• Documentation has been added.
  • example
  • link to example
  • info in documentaiton

[rodja]

It might even be possible to create a ZenohPersistentDict and hence allow a distributed storage without a seperate Redis server. But we should leave that for an other PR.

[evnchn]

Could also make https://nicegui.io/documentation/refreshable#global_scope work, where we faking it with the use of Event

But in another PR.