proc macros: IntoResponse doesn't work for parameters that isn't Result

[niklasad1]

#1057 introduced new a trait for method call responses however there is a an edge-case where the parameter parsing in the proc macro code assumes it can't return Err(e.into) this doesn't work for a type which isn't a Result and the removal of CallError/jsonrpsee::core::Error needs an extra From impl.

These needs to be fixed before releasing in v0.18 and ideally the params parsing could just return PartialResponse directly as handled for subscriptions as well.

Example with the custom error type

pub struct MyError;

impl From<MyError> for ErrorObjectOwned {
	fn from(_: MyError) -> Self {
		ErrorObject::owned(1, "my_error", None::<()>)
	}
}

// This is annoying and shouldn't be needed..
impl From<ErrorObjectOwned> for MyError {
	fn from(_: ErrorObjectOwned) -> MyError {
		MyError
	}
}

#[rpc(server, client, namespace = "t")]
pub trait Api {
	/// Async method call example.
	#[method(name = "getKeys")]
	async fn f(&self, x: usize) -> Result<usize, MyError>;
}

Example with the custom return type

// Serialize impl is not used as the responses are sent out as error.
#[derive(Serialize, Clone)]
pub enum CustomError {
	One,
	Two { custom_data: u32 },
}

impl IntoResponse for CustomError {
	type Output = Self;

	fn into_response(self) -> ResponsePayload<'static, Self::Output> {
           todo!()
        }
	
}

#[rpc(server)]
pub trait Rpc {
        // This won't compile as it would return `Result<usize, ErrorObject>` when parsing `x` in the call
	#[method(name = "method1")]
	async fn method1(&self, x: usize) -> CustomError;
}