Use `jsonpsee` for the rust demo once Ogmios 6.0.1 lands on `ogmios-nixos`

A bug was fixed in Ogmios 6.0.1, which should allow us to use a standard jsonrpc client.
https://ogmios.dev/changelog/#601---2024-01-22

Blocked by: 
https://github.com/mlabs-haskell/ogmios-nixos/pull/1