[fts] Butterworth filter for Force Torque Sensor

• tested on hsr and donbot in real
• test cases with mockup

for understanding:
The @patch decorator in Python is used in unit testing to replace objects in your code with mock objects during the test. This allows you to control the behavior of dependencies and isolate the code under test. It is part of the unittest.mock module.
Here is a brief explanation of how it works:

• @patch replaces the specified object with a mock object.
• The mock object can be configured to return specific values or raise exceptions.
• After the test, the original object is restored.

Example usage:

from unittest.mock import patch

@patch('module.ClassName')
def test_function(mock_class):
    # mock_class is a mock object replacing module.ClassName
    instance = mock_class.return_value
    instance.method.return_value = 'mocked value'

    # Your test code here