bug: `nil` error is passed as `%w` to `fmt.Errrof`

[tzdybal]

https://github.com/rollkit/rollkit/blob/b4cb7b1d2b3595e5792f0edef5df1bcf8dc7be13/state/executor.go#L208-L212

The err passed to fmt.Errorf is always nil so it makes no sense to pass it at all. The error message should be updated.