fix(storage): fix sub level id for time travel

[zwang28]

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What's changed and what's your intention?

Since sublevel ids no longer ensure a monotonically increasing order, and the time travel doesn't keep version delta of compaction, for time travel it's possible the newly inserted sub level id is smaller than the smallest one in the current version. For example:

1. The version has 3 sublevels [1, 2, 3].
2. The version is compacted to 0 sublevels [].
3. A new sublevel is inserted, using committed_epoch as sub_level id. Say committed_epoch is 2, resulting sublevels [2].

The problem is time travel doesn't include the delta from step 2. So in step 3 it will be inserting sublevel 2 into sublevels [1, 2, 3], which will be rejected.

This PR fixes it by setting sub level id later in apply_version_delta, instead of persisting it in delta.

https://risingwave-labs.slack.com/archives/C05MQT5DFTP/p1728718540051539

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[Li0k]

Rest LTGM