publish_to_internal_channel is not threadsafe

まだ誰も着手していません。

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

Here's part of the publish_to_internal_channel func :
``` python
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

iwf/communication.py の publish_to_internal_channel から始め、_to_publish_internal_channel がどのように読み取られ、更新されるかを確認します。並行した publish のカバレッジを追加し、複数のスレッドが同じチャネルに publish したときに値が失われないことを確認します。

索引モデルが issue の本文から書いたものです。