`ServerFnError<T>` should impl `From<E: std::error::Error>` for any `T`

[nicolas-guichard]

Currently, ServerFnError has a blanket From impl to convert from E, but only with the default NoCustomError type:

impl<E: std::error::Error> From<E> for ServerFnError {
    fn from(value: E) -> Self {
        ServerFnError::ServerError(value.to_string())
    }
}

This means we can't easily use ? to convert other errors into a ServerFnError<MyCustomError>.

Instead I think we should provide a blanket impl for any T:

impl<T, E: std::error::Error> From<E> for ServerFnError<T> {
    fn from(value: E) -> Self {
        ServerFnError::ServerError(value.to_string())
    }
}

[gbj]

Feel free to make a PR.