fix: transient table does not work as expected inside explicit transaction

[dantengsky]

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Summary

Enhanced Timestamp Handling in Explicit Transactions

To ensure vacuum operation safety, a critical invariant should be maintained (among others): any successfully committed table snapshot must have all new table data (segments, blocks, indexes) timestamped greater than or equal to its direct predecessor snapshot's timestamp.

The current implementation maintains this invariant but is overly conservative and may cause unexpected exceptions during transient table mutations within an explicit transaction (issue #18159). This issue also occurs when data_retention_time_in_days is set to 0.

This PR:

• Tracks logical transaction begin timestamps for each table within an explicit transaction
• Ensures all new table data during an explicit transaction is marked with timestamps greater than or equal to this logical begin timestamp
• Implements conflict resolution that aborts the current transaction if an already committed conflicting table snapshot has a timestamp greater than the logical transaction begin timestamp of the same table, preserving vacuum safety
• Improves error messages to better describe failure causes, particularly warning users that concurrent modifications to transient tables or tables with minimal retention periods are prone to unresolvable conflicts, with guidance on appropriate adjustments

Adjust Auto-Vacuum Trigger Timing

Auto-vacuum execution now occurs only after successful transaction commit.

Table Meta Timestamp Cache Clearing

Added proactive clearing of table meta timestamp cache before hooks(compaction, index refreshing) execution to resolve issues reported in #18167.

Code Organization Improvements

Test-specific code has been properly annotated with #[cfg(test)] to ensure it's not used outside unit tests, and fixed previous misuses of these test utilities.

• fixes: bug: transient table no work as expected inside explicit transaction #18159
• fixes: bug: auto-compaction of transient tables fails silently #18167

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):

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