new: deepcopy new payload

[joein]

#624 suggests to return deepcopy of payload from scroll/search/etc api, so any changes to the payload returned by these operations won't affect the state of the payload in the db

However, it does not consider a case when the original payload which has been uploaded to db will be changed

e.g.

payload = {"a": {"b": 1}}
...
client.upsert(..., points=[PointStruct(..., payload=payload)])
...
payload["a"]["b"] = 2  # affects the payload in the db

This PR fixes this behaviour