[BUG] `Result` used despite no errors should be handled

[takasaki404]

Here in PayWall returns a Result although no errors should be handled:

    /// Run the resource handler with the payment state attached to the request extensions.
    ///
    /// After running the handler, returns a [`ResponseProcessor`] for further processing.
    pub async fn run_handler<Fun, Fut, Res>(
        mut self,
        handler: Fun,
    ) -> Result<ResponseProcessor<'pw, F, Res>, ErrorResponse>
    where
        Fun: FnOnce(Request<Req>) -> Fut,
        Fut: Future<Output = Response<Res>>,
    {
        self.request
            .extensions_mut()
            .insert(self.payment_state.clone());

        let response = handler(self.request).await;
        Ok(ResponseProcessor {
            paywall: self.paywall,
            response,
            payload: self.payload,
            selected: self.selected,
            payment_state: self.payment_state,
        })
    }