Cleanup sidecars on exit

[ross-weir]

Noticed while developing sidecars that if the main wallet process is killed the sidecar processes (like ergo node) are still running, ensure they're cleaned up.

• Does tauri provide 'on exit' type hooks?
• Rust application 'on exit' type hooks?

[ross-weir]

It's possible this is a side effect of the development environment, I've noticed it happening when ctrl+c'ing the dev server. Might not happen when running the app normally