pstim.py has hard dependency on NI-DAQmx hardware driver with no graceful fallback

[GaneshPatil7517]

@pradeeban
nintan/pstim.py imports nidaqmx at module level and immediately creates a hardware task:

import nidaqmx
from nidaqmx.constants import AcquisitionType
from nidaqmx.stream_writers import DigitalSingleChannelWriter
...
task = nidaqmx.Task()
task.do_channels.add_do_chan("Dev1/port0/line0")

Issues:

• The nidaqmx package is not in requirements.txt

• It crashes on any machine without National Instruments hardware/drivers

• The global uglobal variable is modified by the main thread and read by pwm() thread without any thread synchronization (race condition)

• The pwm() thread runs an infinite while True loop with no way to stop it cleanly

• Device name "Dev1/port0/line0" is hardcoded — should be configurable via concore.params