Serialize Path to JSON when using FileStore

[WardLT]

We get an "unserializable type" error if you use a Path when initializing a FileStore.

  File "/home/lward/miniconda3/envs/voc/lib/python3.10/site-packages/colmena/redis/queue.py", line 397, in send_inputs
    self.outbound.put(result.json(), topic=topic)
  File "/home/lward/miniconda3/envs/voc/lib/python3.10/site-packages/colmena/models.py", line 218, in json
    return json.dumps(data, default=proxy_json_encoder)
  File "/home/lward/miniconda3/envs/voc/lib/python3.10/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/home/lward/miniconda3/envs/voc/lib/python3.10/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/home/lward/miniconda3/envs/voc/lib/python3.10/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/home/lward/miniconda3/envs/voc/lib/python3.10/site-packages/colmena/proxy.py", line 46, in proxy_json_encoder
    raise TypeError(f'Unserializable type: {type(proxy)}')
TypeError: Unserializable type: <class 'pathlib.PosixPath'>

[gpauloski]

Is it the proxystore_kwargs where the Path object is that fails?

colmena/colmena/models.py

Line 163 in d638178

proxystore_kwargs: Optional[Dict] = Field(None, description="Kwargs to reinitialize ProxyStore backend")

It's an easy cast to str when initializing the FileStore. That happens on the user-side, though, and not the library-side so maybe we need to extend the warnings/errors in proxy_json_encoder to note args to ProxyStore Stores need to be JSON serializable if the user selects JSON serialization.