Add tests for pokeys_py component

[zarfld]

Related to #31

Add comprehensive tests for all functionalities of the pokeys_py component.

• Digital I/O: Add tests for handling inversion parameters in tests/test_digital_io.py.
• CAN Bus Communication: Add tests for CAN bus communication in tests/test_can_bus.py.
• PoRelay8 Interaction: Add tests for interaction with PoRelay8 in tests/test_porelay8.py.
• Analog I/O: Expand tests for error conditions and edge cases in tests/test_analog_io.py.
• Counter: Expand tests for error conditions and edge cases in tests/test_counter.py.
• PEv2 Motion Control: Expand tests for error conditions and edge cases in tests/test_pev2_motion_control.py.
• PoNET: Expand tests for error conditions and edge cases in tests/test_ponet.py.
• PWM: Expand tests for error conditions and edge cases in tests/test_pwm.py.

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