publish_to_internal_channel is not threadsafe

https://github.com/indeedeng/iwf-python-sdk/blob/a13c309d58bb553a3ee27c85899f7f25c500d877/iwf/communication.py#L51

Here's part of the publish_to_internal_channel func :

def publish_to_internal_channel(self, channel_name: str, value: Any = None):     
    ...   
    vals = self._to_publish_internal_channel.get(channel_name)
    if vals is None:
        vals = []
    vals.append(self._object_encoder.encode(value))
    self._to_publish_internal_channel[channel_name] = vals

When multiple threads hitting this function, it could have a race condition where
Thread A gets vals = [1,2,3]
Thread B gets vals = [1,2,3]
Thread A updates it to be [1,2,3,4]
Thread B updates it to be [1,2,3,5]
Here we lost 4 permanently

Start in iwf/communication.py at publish_to_internal_channel and review how _to_publish_internal_channel is read and updated. Add coverage for concurrent publishes, then verify that no values are lost when multiple threads publish to the same channel.