Fix RJob failure propagation and submission logging

[JifeiShan]

Summary

• propagate non-zero runner task results so the OpenCompass process fails instead of only logging errors
• emit an explicit RJob submitted event only after rjob submit succeeds
• avoid logging an empty command error for successful submissions

This prevents planned RJob names whose submission failed from being interpreted as successfully completed jobs by external lifecycle integrations.

Tests

• python3 tests/runners/test_base.py
• python3 -m compileall -q opencompass/runners/base.py opencompass/runners/rjob.py tests/runners/test_base.py
• git diff --check