feat: quit checkpoint engine when error occurs

[specture724]

resolve #38

send an Exception to PS when update_weights_from_ipc execute run failed. _update_per_bucket needs to ensure all processes not to get an Exception before continuing next updating iteration

[Copilot]

Pull Request Overview

This PR implements error handling in the checkpoint worker process to ensure graceful shutdown when errors occur during weight updates. The changes propagate exceptions from worker processes back to the parameter server, allowing coordinated error handling across all distributed ranks.

Key Changes:

• Worker processes now send exception objects to the parameter server when run() fails, instead of silently failing
• Parameter server synchronizes error states across all ranks before continuing, ensuring no rank proceeds if any rank encounters an error
• Process group cleanup moved to a finally block to ensure proper resource cleanup even when errors occur

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
checkpoint_engine/worker.py	Added try-except block to catch exceptions during weight updates and send them back to the parameter server
checkpoint_engine/ps.py	Modified error handling to collect responses from all ranks and raise error if any rank failed; moved cleanup to finally block
tests/test_error_quit.py	Added integration test that verifies proper error propagation and process termination when worker process encounters runtime errors

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