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

sgl-router/src/protocols/common.rs

@@ -0,0 +1,36 @@
+// Common types shared across all protocol implementations
+
+use serde::{Deserialize, Serialize};
+
+/// Helper function for serde default value
+pub fn default_true() -> bool {
+    true
+}
+
+/// Common trait for all generation requests across different APIs
+pub trait GenerationRequest: Send + Sync {
+    /// Check if the request is for streaming
+    fn is_stream(&self) -> bool;
+
+    /// Get the model name if specified
+    fn get_model(&self) -> Option<&str>;
+
+    /// Extract text content for routing decisions
+    fn extract_text_for_routing(&self) -> String;
+}
+
+/// Helper type for string or array of strings
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum StringOrArray {
+    String(String),
+    Array(Vec<String>),
+}
+
+/// LoRA adapter path - can be single path or batch of paths (SGLang extension)
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum LoRAPath {
+    Single(Option<String>),
+    Batch(Vec<Option<String>>),
+}