Fail fast when overlap wait times out

[TianyeGGBond]

Context

_wait_for_overlap_engines_offloaded is the safety gate before training resumes on GPUs that may have just been used by inference engines. If the engine state probe fails or the wait times out, continuing can surface later as a less-informative train wake-up OOM.

Change

• raise when engine state polling fails
• raise when engines do not reach a safe state before the timeout
• raise when the free-memory gate times out

Validation

• python -m py_compile rlix/pipeline/miles_pipeline.py