Fix CommsLogger.stop_profiling_comms not disabling global profiling

[vineethsaivs]

What

CommsLogger.stop_profiling_comms() set self.prof_all = True, the same value start_profiling_comms() sets, so calling stop was a no-op:

def start_profiling_comms(self):
    self.prof_all = True

def stop_profiling_comms(self):
    self.prof_all = True   # should be False

prof_all is the flag that makes the comms logger profile every collective (deepspeed/comm/comm.py gates on ... or comms_logger.prof_all or ...). Because stop set it back to True, once global comm profiling was started it could never be turned off. The sibling pair in the same class, start_profiling_op / stop_profiling_op, correctly adds then removes ops, which confirms the intended start=on / stop=off asymmetry.

Fix

Set prof_all = False in stop_profiling_comms().

Test

Added tests/unit/comm/test_comms_logger.py, a CPU-only unit test that starts then stops comm profiling and asserts prof_all ends up False. It fails before the change (stays True) and passes after.

[tohtana]

Great catch! This looks good to me.
Can you just change the license header to "# Copyright (c) DeepSpeed Team."? DeepSpeed is not under Microsoft anymore.