fix(storage): avoid collecting vacuum2 result files

[dantengsky]

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

Summary

vacuum2 previously accumulated every deleted block, index, segment, and snapshot path in a Vec<String>, even when invoked through CALL system$fuse_vacuum2(...), where the result was discarded. This made peak memory grow with the total number of deleted files.

This PR:

• Changes the vacuum2 handler result from Result<Vec<String>> to Result<()>
• Removes deleted-path accumulation from block GC and metadata cleanup
• Retains count-based status reporting through BlockGcStats
• Makes direct SELECT * FROM fuse_vacuum2(...) return zero rows instead of per-file paths
• Adds Rust and SQL regression coverage for the zero-row result while continuing to verify storage cleanup

The disabled fake-time harness (8_faked_time_prepare / 9_faked_time) and its dead CI action/script are removed. Its useful coverage now runs in the normal Rust unit-test CI: deterministic retention-cutoff boundary tests plus an EE integration test that persists a middle-snapshot LVT and verifies respect_flash_back=true selects that snapshot as the GC root.

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):

The behavior change is limited to callers that consume per-file rows from SELECT * FROM fuse_vacuum2(...); the documented operational CALL system$fuse_vacuum2(...) path continues to report success without file details.

AI assistance

• AI usage: An AI coding agent investigated the vacuum2 result construction, drafted the implementation and regression tests, and ran the validation commands listed above
• Responsible human: @dantengsky
• The responsible human has read every line of this diff and can explain each change

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This change is 

[chatgpt-codex-connector]

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[dantengsky]

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Reviewed commit: b1b53c8dbb

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