lisa._assets.kmodules.lisa: Improve FFI bindings

FEATURE

* Implement IntoFfi for &str. This is achieved by using struct rust_str
  rather than using const char*, as the latter only allowed a FromFfi
  implementation.

* Pretty print error codes wrapper in ErrorCode. This includes the
  NegativeError type that provides a binding to the PTR_ERR() kernel
  API.