[router] add worker abstraction (#7960)

sgl-router/src/core/mod.rs

@@ -0,0 +1,16 @@
+//! Core abstractions for the SGLang router
+//!
+//! This module contains the fundamental types and traits used throughout the router:
+//! - Worker trait and implementations
+//! - Error types
+//! - Common utilities
+
+pub mod error;
+pub mod worker;
+
+// Re-export commonly used types at the module level
+pub use error::{WorkerError, WorkerResult};
+pub use worker::{
+    start_health_checker, BasicWorker, HealthChecker, Worker, WorkerCollection, WorkerFactory,
+    WorkerLoadGuard, WorkerType,
+};