[Design]: Signer event loop

[netrome]

Design - Signer event loop

Context

While we have a high level design for the signer in #44, along with a detailed state model in #60, there is a lot of details that goes into the actual signer event loop and how we intend the signer to react to state updates and messages from other signers. We should write down some flow-charts illustrating how we intend the signer to behave before beginning the implementation of it.

Definition of done

We have a detailed design with appropriate illustrations showcasing from a high-level view how the signer event loop is intended to work.

[netrome]

Excalidraw draft