feat: implement reasoning_tokens tracking and enhanced usage logging

src/providers/helpers.rs

@@ -254,6 +254,11 @@ pub fn parse_openai_response(resp_json: &Value, model: String) -> Result<Provide
     let completion_tokens = usage["completion_tokens"].as_u64().unwrap_or(0) as u32;
     let total_tokens = usage["total_tokens"].as_u64().unwrap_or(0) as u32;
 
+    // Extract reasoning tokens
+    let reasoning_tokens = usage["completion_tokens_details"]["reasoning_tokens"]
+        .as_u64()
+        .unwrap_or(0) as u32;
+
     // Extract cache tokens — try OpenAI/Grok format first, then DeepSeek format
     let cache_read_tokens = usage["prompt_tokens_details"]["cached_tokens"]
         .as_u64()
@@ -271,6 +276,7 @@ pub fn parse_openai_response(resp_json: &Value, model: String) -> Result<Provide
         tool_calls,
         prompt_tokens,
         completion_tokens,
+        reasoning_tokens,
         total_tokens,
         cache_read_tokens,
         cache_write_tokens,
@@ -295,6 +301,10 @@ pub fn parse_openai_stream_chunk(
         let completion_tokens = u["completion_tokens"].as_u64().unwrap_or(0) as u32;
         let total_tokens = u["total_tokens"].as_u64().unwrap_or(0) as u32;
 
+        let reasoning_tokens = u["completion_tokens_details"]["reasoning_tokens"]
+            .as_u64()
+            .unwrap_or(0) as u32;
+
         let cache_read_tokens = u["prompt_tokens_details"]["cached_tokens"]
             .as_u64()
             .or_else(|| u["prompt_cache_hit_tokens"].as_u64())
@@ -305,6 +315,7 @@ pub fn parse_openai_stream_chunk(
         Some(StreamUsage {
             prompt_tokens,
             completion_tokens,
+            reasoning_tokens,
             total_tokens,
             cache_read_tokens,
             cache_write_tokens,