feat: Improve service manager testing and error handling

- Add comprehensive testing instructions to README.
- Improve error handling in examples to prevent crashes.
- Enhance launchctl error handling for production safety.
- Improve zinit error handling for production safety.
- Remove obsolete plan_to_fix.md file.
- Update Rhai integration tests for improved robustness.
- Improve service manager creation on Linux with systemd fallback.

service_manager/examples/service_spaghetti.rs

@@ -10,7 +10,13 @@ use std::thread;
 use std::time::Duration;
 
 fn main() {
-    let manager = create_service_manager();
+    let manager = match create_service_manager() {
+        Ok(manager) => manager,
+        Err(e) => {
+            eprintln!("Error: Failed to create service manager: {}", e);
+            return;
+        }
+    };
     let service_name = "com.herocode.examples.spaghetti";
 
     let service_config = ServiceConfig {

service_manager/examples/simple_service.rs

@@ -5,7 +5,13 @@ use std::time::Duration;
 
 fn main() {
     // 1. Create a service manager for the current platform
-    let manager = create_service_manager();
+    let manager = match create_service_manager() {
+        Ok(manager) => manager,
+        Err(e) => {
+            eprintln!("Error: Failed to create service manager: {}", e);
+            return;
+        }
+    };
 
     // 2. Define the configuration for our new service
     let service_name = "com.herocode.examples.simpleservice";