Improved JSONSchemaParser performance (#93)

* Improving backslash escaping performance, based on github discussion

* Taking the finished parser's last parsed string before discarding it

lmformatenforcer/jsonschemaparser.py

@@ -91,6 +91,15 @@ def add_character(self, new_character: str) -> CharacterLevelParser:
                 option_json_schema_parsers.append(option_parser)
             return UnionParser(option_json_schema_parsers)
 
+        # For some performance optimizations to work, we want to make sure we don't leave irrelevant
+        # objects at the top of the stack, which we know will be passed over next timestep
+        new_object_stack = updated_parser.object_stack
+        while new_object_stack and new_object_stack[-1].can_end() and new_object_stack[-1].get_allowed_characters() == '':
+            finished_receiver = new_object_stack[-1]
+            if isinstance(finished_receiver, StringParsingState):
+                updated_parser.last_parsed_string = finished_receiver.parsed_string
+            del new_object_stack[-1]
+
         return updated_parser
 
     def get_allowed_characters(self) -> str: