[router] add dsr1, kimi, and qwen reasoning parser (#9353)

sgl-router/src/reasoning_parser/traits.rs

@@ -96,14 +96,14 @@ pub struct ParserConfig {
     /// The token that marks the end of reasoning content.
     pub think_end_token: String,
 
-    /// Whether to force all text to be treated as reasoning.
-    pub force_reasoning: bool,
-
     /// Whether to stream reasoning content as it arrives.
     pub stream_reasoning: bool,
 
     /// Maximum buffer size in bytes.
     pub max_buffer_size: usize,
+
+    /// Initial state for in_reasoning flag (fixed per parser type).
+    pub initial_in_reasoning: bool,
 }
 
 impl Default for ParserConfig {
@@ -111,9 +111,9 @@ impl Default for ParserConfig {
         Self {
             think_start_token: "<think>".to_string(),
             think_end_token: "</think>".to_string(),
-            force_reasoning: false,
             stream_reasoning: true,
-            max_buffer_size: 65536, // 64KB default
+            max_buffer_size: 65536,      // 64KB default
+            initial_in_reasoning: false, // Default to false (explicit reasoning)
         }
     }
 }