Remove Redis as a dependency

[marsupialtail]

The current data plane uses Ray for same machine comms and Redis for inter-machine comms.

Both should be replaced by a custom Arrow Flight server, with two benefits:

• No more disk flushing and reading on demand on same machine
• No more pickle.loads or pickle.dumps
• Possibility for more custom behavior
• Better control from Python side

[marsupialtail]

moved data movement to flight server in PR #6