fix: dup split assignment in source

[tabVersion]

I hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

prev #18134 (#18157, #18158) does not fix the case completely.

In the prev fix, we check each mutation and removed the dup one from the assignment. But we have no way to know the prev assignment and it can cause the dup assignment as well.

Giving a more concrete example here

T0: actor_1(split_1, split_2), actor_2(split_3)

and we have a dup assignment, the mutation looks like {"actor_1"; ["split_1, split_2"], "actor_2": [split_2, split_3]}, after the check impl, the mutation may look like {"actor_1"; ["split_1], "actor_2": [split_2, split_3]} as we RANDOMLY remove the dup split from the assignment.

So actor_1 knows it should remove split_2 but it still needs to write the latest offset to the storage. But actor_2 ought to write split_2 with the initial offset to the storage to mark it as applying the change successfully.
As a result, we get a dup write on the same key and same epoch panic in the compactor.

This pr handles this case by wrapping the dup split detected split_change_mutation with pause/resume. Separating the two writes to different epoches.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added test labels as necessary. See details.
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• My PR contains breaking changes. (If it deprecates some features, please create a tracking issue to remove them in the future).
• All checks passed in ./risedev check (or alias, ./risedev c)
• My PR changes performance-critical code. (Please run macro/micro-benchmarks and show the results.)

• My PR contains critical fixes that are necessary to be merged into the latest release. (Please check out the details)

Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

If this PR includes changes that directly affect users or other significant modifications relevant to the community, kindly draft a release note to provide a concise summary of these changes. Please prioritize highlighting the impact these changes will have on users.

[shanicky]

LGTM