feat: Add service manager support

- Add a new service manager crate for dynamic service management
- Integrate service manager with Rhai for scripting
- Provide examples for circle worker management and basic usage
- Add comprehensive tests for service lifecycle and error handling
- Implement cross-platform support for macOS and Linux (zinit/systemd)

src/lib.rs

@@ -64,6 +64,9 @@ pub use sal_redisclient as redisclient;
 #[cfg(feature = "rhai")]
 pub use sal_rhai as rhai;
 
+#[cfg(feature = "service_manager")]
+pub use sal_service_manager as service_manager;
+
 #[cfg(feature = "text")]
 pub use sal_text as text;