fix: pass raw bytes to Dart/R parsers instead of decoded str

tree-sitter-language-pack 1.12.5 enforces that Parser.parse() receives
bytes or a callable, not str, breaking the Dart and R parsers which
decoded source to str before parsing. Every other language parser
already passes raw bytes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: GoodbyePlanet

server/parser/dart.py

@@ -283,7 +283,7 @@ def language(self) -> str:
         return "dart"
 
     def parse_file(self, source: bytes, file_path: str) -> list[CodeSymbol]:
-        tree = self._parser.parse(source.decode("utf-8", errors="replace"))
+        tree = self._parser.parse(source)
         symbols: list[CodeSymbol] = []
         _walk(root_node_for_tree(tree), source, file_path, symbols)
         return symbols

server/parser/r.py

@@ -124,7 +124,7 @@ def language(self) -> str:
         return "r"
 
     def parse_file(self, source: bytes, file_path: str) -> list[CodeSymbol]:
-        tree = self._parser.parse(source.decode("utf-8", errors="replace"))
+        tree = self._parser.parse(source)
         symbols: list[CodeSymbol] = []
         for child in root_node_for_tree(tree).children:
             if child.type == "binary_operator":