Move appendable object creation outside transactions

[jiangxinmeng1]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #25533

What this PR does / why we need it:

• Create appendable objects as committed catalog entries from the appender path using TxnMgr.Now(), without attaching them to the active transaction.
• Rebuild missing appendable objects during WAL replay from append command row IDs, then normalize their create timestamp after replay using the minimum observed commit timestamp.
• Preserve apply-table-data semantics for appendable stats and reject unexpected transactional appendable-object create entries while keeping old WAL replay compatible.
• Added/updated tests around appendable object replay and apply-table-data behavior.

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