chore: ensuring all imperfect blocks are compacted

[zhyass]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

When checking the compaction block limit, we now verify the number of imperfect blocks among the selected blocks.
Once reached for imperfect blocks, triggers one final segment acquisition before stopping. This “+1” segment behaviour ensures boundary blocks are not missed and avoids off-by-one omissions.

Refactors the is_limit_reached method to return an explicit state enum (CompactLimitState) with values: Continue, ReachedBlockLimit, ReachedSegmentLimit. This clarifies the intent of each stop condition and aligns the control flow with the outer loop logic.

Improves readability of the compaction loop by handling the “take one more” state outside the immediate stop condition, thus making the workflow more predictable and maintainable.

This change ensures that auto-compaction covers all eligible segments/blocks without accidentally skipping near-limit items, and also tightly bounds resource usage by segments.

Fixes: #18859

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

---

This change is 

[github-actions]

Docker Image for PR

• tag: pr-18860-5d62881-1760879530

note: this image tag is only available for internal use.

[github-actions]

Docker Image for PR

• tag: pr-18860-fdab881-1760964116

note: this image tag is only available for internal use.

[github-actions]

Docker Image for PR

• tag: pr-18860-70ab357-1761217919

note: this image tag is only available for internal use.