via_device support, improved ergonomics

[zoe-codez]

Changes

• added the ability to create secondary devices and map to entities
• added the ability to define reactive config values in synapse entities (allow listed keys)
• converted synapse entities from a basic object to a 🪄 proxy
  • runtime settable configuration properties can now be read/written from the proxy
  • existing keys from the current object are matched in the proxy
• fix entity.onUpdate
• improved typing around string unions with entities (more to go)

Checklist

• Read the contribution guide and accept the
  code of conduct
• Readme and docs (updated or not needed)
• Tests (added, updated or not needed)