[Task] Add priority scheduling CIs for preemption path

Checklist

• If this is not a feature request but a general question, please start a discussion at https://github.com/sgl-project/sglang/discussions. Otherwise, it will be closed.
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Motivation

There is a number token and request level memory accounting issues reported and fixed by the community recently. It would be good to complement them with robust CI tests.

Context:

1. https://github.com/sgl-project/sglang/pull/12494
2. https://github.com/sgl-project/sglang/pull/13142
3. https://github.com/sgl-project/sglang/pull/13201; https://github.com/sgl-project/sglang/issues/13111 (TestRemTotalTokenOffsetBug)
4. https://github.com/sgl-project/sglang/blob/5ef728716b2c1159bbb7cd5c098e7720137354ce/python/sglang/srt/managers/schedule_policy.py#L666-L668 - cover this case

Related resources

No response