Fixes according to review notes

lark/lark.py

@@ -62,20 +62,20 @@ class LarkOptions(Serialize):
     regex: bool
     g_regex_flags: int
     keep_all_tokens: bool
-    tree_class: Callable
+    tree_class: Optional[Callable[[str, Sequence], Any]]
     parser: _ParserArgType
     lexer: _LexerArgType
     ambiguity: 'Literal["auto", "resolve", "explicit", "forest"]'
     postlex: Optional[PostLex]
     priority: 'Optional[Literal["auto", "normal", "invert"]]'
     lexer_callbacks: Dict[str, Callable[[Token], Token]]
     use_bytes: bool
+    ordered_sets: bool
     edit_terminals: Optional[Callable[[TerminalDef], TerminalDef]]
     import_paths: 'List[Union[str, Callable[[Union[None, str, PackageResource], str], Tuple[str, str]]]]'
     source_path: Optional[str]
-    ordered_sets: bool
 
-    OPTIONS_DOC = """
+    OPTIONS_DOC = r"""
     **===  General Options  ===**
 
     start
@@ -143,7 +143,7 @@ class LarkOptions(Serialize):
     use_bytes
             Accept an input of type ``bytes`` instead of ``str``.
     ordered_sets
-            Should Earley use ordered-sets to achieve stable output (~10%% slower than regular sets. Default: True)
+            Should Earley use ordered-sets to achieve stable output (~10% slower than regular sets. Default: True)
     edit_terminals
             A callback for editing the terminals before parse.
     import_paths

lark/parser_frontends.py

@@ -1,7 +1,7 @@
 from typing import Any, Callable, Dict, Optional, Collection
 
 from .exceptions import ConfigurationError, GrammarError, assert_config
-from .utils import get_regexp_width, Serialize, OrderedSet
+from .utils import get_regexp_width, Serialize
 from .parsers.grammar_analysis import GrammarAnalyzer
 from .lexer import LexerThread, BasicLexer, ContextualLexer, Lexer
 from .parsers import earley, xearley, cyk