Support Separate Process for Reward Computation via Inter-Process Communication

[SeonghwanSeo]

Implement Inter-Process Communication (IPC) Module Between GFlowNet and Reward Function

This PR introduces an inter-process communication (IPC) module that enables reward computation in a separate process from GFlowNet.

Implementation Details

The implementation includes three key classes (gflownet.utils.communication):

• IPCModule – A core module for communication between GFlowNet and the reward function.
• IPCTask – A GFlowNet task with IPCModule.
• RewardModule – A reward function with IPCModule.

Supported IPC Methods

The current implementation supports three IPC methods:

1. NetworkIPC – Uses a TCP/IP protocol (without file system). Recommended.
2. FileSystemIPC – Uses the file system with serialized data. Recommended.
3. FileSystemIPC_CSV – Uses the file system (csv format). It may be useful for non-Python reward functions or human feedback integration.

User can setup IPC at config.communication.

There are two example scripts: src/gflownet/tasks/seh_frag_ipc.py, src/gflownet/tasks/seh_frag_moo_ipc.py

Impact on Existing Code

This PR introduces minimal changes to the existing codebase. The key differences compared to the latest trunk are:

1. Added a numpy version constraint (<2.0.0) in pyproject.toml.
2. Add a field communication to config.