Add LODR support to online and offline recognizers (#2026)

This PR integrates LODR (Level-Ordered Deterministic Rescoring) support from Icefall into both online and offline recognizers, enabling LODR for LM shallow fusion and LM rescore.

- Extended OnlineLMConfig and OfflineLMConfig to include lodr_fst, lodr_scale, and lodr_backoff_id.
- Implemented LodrFst and LodrStateCost classes and wired them into RNN LM scoring in both online and offline code paths.
- Updated Python bindings, CLI entry points, examples, and CI test scripts to accept and exercise the new LODR options.

sherpa-onnx/csrc/online-lm-config.h

@@ -18,18 +18,26 @@ struct OnlineLMConfig {
   float scale = 0.5;
   int32_t lm_num_threads = 1;
   std::string lm_provider = "cpu";
+  std::string lodr_fst;
+  float lodr_scale = 0.01;
+  int32_t lodr_backoff_id = -1;  // -1 means not set
   // enable shallow fusion
   bool shallow_fusion = true;
 
   OnlineLMConfig() = default;
 
   OnlineLMConfig(const std::string &model, float scale, int32_t lm_num_threads,
-                 const std::string &lm_provider, bool shallow_fusion)
+                 const std::string &lm_provider, bool shallow_fusion,
+                 const std::string &lodr_fst, float lodr_scale,
+                 int32_t lodr_backoff_id)
       : model(model),
         scale(scale),
         lm_num_threads(lm_num_threads),
         lm_provider(lm_provider),
-        shallow_fusion(shallow_fusion) {}
+        shallow_fusion(shallow_fusion),
+        lodr_fst(lodr_fst),
+        lodr_scale(lodr_scale),
+        lodr_backoff_id(lodr_backoff_id) {}
 
   void Register(ParseOptions *po);
   bool Validate() const;