[router]restructure protocol modules for better organization (#9321)

sgl-router/src/server.rs

@@ -1,7 +1,10 @@
 use crate::config::RouterConfig;
 use crate::logging::{self, LoggingConfig};
 use crate::metrics::{self, PrometheusConfig};
-use crate::openai_api_types::{ChatCompletionRequest, CompletionRequest, GenerateRequest};
+use crate::protocols::{
+    generate::GenerateRequest,
+    openai::{chat::ChatCompletionRequest, completions::CompletionRequest},
+};
 use crate::routers::{RouterFactory, RouterTrait};
 use crate::service_discovery::{start_service_discovery, ServiceDiscoveryConfig};
 use axum::{