Adding warm up for Zipformer2 (#766)

Signed-off-by: manickavela1998@gmail.com <manickavela1998@gmail.com>

sherpa-onnx/csrc/online-recognizer.h

@@ -162,6 +162,15 @@ class OnlineRecognizer {
     DecodeStreams(ss, 1);
   }
 
+  /**
+   * Warmups up onnxruntime sessions by apply optimization and
+   * allocating memory prior
+   *
+   * @param warmup Number of warmups.
+   * @param mbs : max-batch-size Max batch size for the models
+  */
+  void WarmpUpRecognizer(int32_t warmup, int32_t mbs) const;
+
   /** Decode multiple streams in parallel
    *
    * @param ss Pointer array containing streams to be decoded.