修正示例中的三轴力单位显示

避免未标定读数被示例标成 N，并让 Finger 示例读取 SDK 的每轴单位。已通过相关测试和语法检查。

tests/test_finger_runtime.py

@@ -123,6 +123,7 @@ def test_tactile_processor_push_frame_uses_default_valid_mask():
 
         def __init__(self):
             self.calls = []
+            self.force_units = ("N", "raw", "raw")
             self.frame = None
             self.img = None
             self.flow = None
@@ -146,6 +147,7 @@ def test_tactile_processor_push_frame_uses_default_valid_mask():
     result = tactile.push_frame(frame, already_gray=True)
 
     assert result == "ok"
+    assert tactile.force_units == ("N", "raw", "raw")
     assert sensor.calls[0]["frame"] is frame
     assert sensor.calls[0]["already_processed"] is True
     assert sensor.calls[0]["already_gray"] is True