Remove Anyhow::Result in system_piping.rs example (#7657)

# Objective

Fixes: #7610 

## Solution

- Return a specific error type

Author: foxzool

examples/ecs/system_piping.rs

@@ -1,8 +1,8 @@
 //! Illustrates how to make a single system from multiple functions running in sequence,
 //! passing the output of the first into the input of the next.
 
-use anyhow::Result;
 use bevy::prelude::*;
+use std::num::ParseIntError;
 
 use bevy::log::LogPlugin;
 use bevy::utils::tracing::Level;
@@ -31,20 +31,20 @@ struct Message(String);
 struct OptionalWarning(Result<(), String>);
 
 // This system produces a Result<usize> output by trying to parse the Message resource.
-fn parse_message_system(message: Res<Message>) -> Result<usize> {
-    Ok(message.parse::<usize>()?)
+fn parse_message_system(message: Res<Message>) -> Result<usize, ParseIntError> {
+    message.parse::<usize>()
 }
 
 // This system produces a Result<()> output by trying to parse the Message resource.
-fn parse_error_message_system(message: Res<Message>) -> Result<()> {
+fn parse_error_message_system(message: Res<Message>) -> Result<(), ParseIntError> {
     message.parse::<usize>()?;
     Ok(())
 }
 
 // This system takes a Result<usize> input and either prints the parsed value or the error message
 // Try changing the Message resource to something that isn't an integer. You should see the error
 // message printed.
-fn handler_system(In(result): In<Result<usize>>) {
+fn handler_system(In(result): In<Result<usize, ParseIntError>>) {
     match result {
         Ok(value) => println!("parsed message: {value}"),
         Err(err) => println!("encountered an error: {err:?}"),