nipanel: Extract typing backports into a submodule

src/nipanel/_panel.py

@@ -1,21 +1,14 @@
 from __future__ import annotations
 
-import sys
 from abc import ABC
 from types import TracebackType
-from typing import TYPE_CHECKING
 
 import grpc
 from ni_measurement_plugin_sdk_service.discovery import DiscoveryClient
 from ni_measurement_plugin_sdk_service.grpc.channelpool import GrpcChannelPool
 
 from nipanel._panel_client import PanelClient
-
-if TYPE_CHECKING:
-    if sys.version_info >= (3, 11):
-        from typing import Self
-    else:
-        from typing_extensions import Self
+from nipanel._typing import Self
 
 
 class Panel(ABC):

src/nipanel/_panel_client.py

@@ -4,20 +4,14 @@
 
 import logging
 import threading
-from typing import TYPE_CHECKING, Callable, TypeVar
 
 import grpc
 from ni.pythonpanel.v1.python_panel_service_pb2 import ConnectRequest, DisconnectRequest
 from ni.pythonpanel.v1.python_panel_service_pb2_grpc import PythonPanelServiceStub
 from ni_measurement_plugin_sdk_service.discovery import DiscoveryClient
 from ni_measurement_plugin_sdk_service.grpc.channelpool import GrpcChannelPool
 
-_T = TypeVar("_T")
-
-if TYPE_CHECKING:
-    from typing_extensions import ParamSpec
-
-    _P = ParamSpec("_P")
+from nipanel._typing import Callable, _T, _P
 
 
 _logger = logging.getLogger(__name__)

src/nipanel/_typing.py

@@ -0,0 +1,29 @@
+"""Single source for typing backports to avoid depending on typing_extensions at run time."""
+
+from __future__ import annotations
+
+import sys
+from typing import TYPE_CHECKING, Callable
+
+if sys.version_info >= (3, 11):
+    from typing import Self
+elif TYPE_CHECKING:
+    from typing_extensions import Self
+else:
+    Self = None
+
+if TYPE_CHECKING:
+    from typing_extensions import ParamSpec, TypeVar
+
+    _P = ParamSpec("_P")
+    _T = TypeVar("_T")
+else:
+    _P = None
+    _T = None
+
+__all__ = [
+    "Callable",
+    "Self",
+    "_P",
+    "_T",
+]