Track token scores (#571)

* add export of per-token scores (ys, lm, context)

- for best path of the modified-beam-search decoding of transducer

* refactoring JSON export of OnlineRecognitionResult, extending pybind11 API of OnlineRecognitionResult

* export per-token scores also for greedy-search (online-transducer)

- export un-scaled lm_probs (modified-beam search, online-transducer)
- polishing

* fill lm_probs/context_scores only if LM/ContextGraph is present (make Result smaller)

sherpa-onnx/python/csrc/online-recognizer.cc

@@ -28,7 +28,26 @@ static void PybindOnlineRecognizerResult(py::module *m) {
           [](PyClass &self) -> float { return self.start_time; })
       .def_property_readonly(
           "timestamps",
-          [](PyClass &self) -> std::vector<float> { return self.timestamps; });
+          [](PyClass &self) -> std::vector<float> { return self.timestamps; })
+      .def_property_readonly(
+          "ys_probs",
+          [](PyClass &self) -> std::vector<float> { return self.ys_probs; })
+      .def_property_readonly(
+          "lm_probs",
+          [](PyClass &self) -> std::vector<float> { return self.lm_probs; })
+      .def_property_readonly(
+          "context_scores",
+          [](PyClass &self) -> std::vector<float> {
+            return self.context_scores;
+      })
+      .def_property_readonly(
+          "segment",
+          [](PyClass &self) -> int32_t { return self.segment; })
+      .def_property_readonly(
+          "is_final",
+          [](PyClass &self) -> bool { return self.is_final; })
+      .def("as_json_string", &PyClass::AsJsonString,
+            py::call_guard<py::gil_scoped_release>());
 }
 
 static void PybindOnlineRecognizerConfig(py::module *m) {