Add a reset method

Author: riedgar-ms

guidance/models/_model.py

@@ -207,6 +207,9 @@ def __init__(self, tokenizer, compute_log_probs=False):
 
         self.metrics = GuidanceEngineMetrics()
 
+    def reset_metrics(self):
+        self.metrics = GuidanceEngineMetrics()
+
     def start(self, parser, grammar, ensure_bos_token=True):
         """Start processing parser state executed through the grammar.