mypy: use implicit-optional (#31590)

* mypy: set implicit-optional = true

* find and replace '| None = None' -> '= None' in function args

common/file_helpers.py

@@ -23,7 +23,7 @@ class CallbackReader:
 
 
 @contextlib.contextmanager
-def atomic_write_in_dir(path: str, mode: str = 'w', buffering: int = -1, encoding: str | None = None, newline: str | None = None,
+def atomic_write_in_dir(path: str, mode: str = 'w', buffering: int = -1, encoding: str = None, newline: str = None,
                         overwrite: bool = False):
   """Write to a file atomically using a temporary file in the same directory as the destination file."""
   dir_name = os.path.dirname(path)

common/prefix.py

@@ -8,7 +8,7 @@ from openpilot.system.hardware.hw import Paths
 from openpilot.system.hardware.hw import DEFAULT_DOWNLOAD_CACHE_ROOT
 
 class OpenpilotPrefix:
-  def __init__(self, prefix: str | None = None, clean_dirs_on_exit: bool = True, shared_download_cache: bool = False):
+  def __init__(self, prefix: str = None, clean_dirs_on_exit: bool = True, shared_download_cache: bool = False):
     self.prefix = prefix if prefix else str(uuid.uuid4().hex[0:15])
     self.msgq_path = os.path.join('/dev/shm', self.prefix)
     self.clean_dirs_on_exit = clean_dirs_on_exit