[worker] fix: OOM on first iteration in multi-turn RL

[zTonyZhao]

What does this PR do?

Fix issue #2189.

This bug was introduced in #1911, which relocated resume_memory_occupation in resharding phase before calling get_torch_device().empty_cache().

Calling resume_memory_occupation without emptying cache before will cause OOM on resharding phase of the first iteration, which prevents the example run_qwen2.5-3b_gsm8k_multiturn to run.

Re-adding get_torch_device().empty_cache() solves the problem, and allows the example to run again.

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