Undo deletion_queue insert on failure in next tx

[sfc-gh-npuka]

How it works:

Transaction N:
  PRE_COMMIT:
    1. UndoFailedRestCatalogDeletionQueueEntries()
       → DELETEs paths from deletion_queue that failed in tx N-1
    2. ApplyIcebergMetadataChanges()
       → InsertDeletionQueueRecord(metadataPath, ...) as before (optimistic)
       → reports the inserted path back via output parameter
    3. The path is saved in RestCatalogRequestPerTable.deletionQueueMetadataPath
  COMMIT:
    4. PostAllRestCatalogRequests() → HTTP POST to REST catalog
       If 204: done (deletion queue entry was correct all along)
       If not 204: save all deletionQueueMetadataPath values to
               FailedRestCatalogDeletionPaths (TopMemoryContext)

Transaction N+1:
  PRE_COMMIT:
    1. UndoFailedRestCatalogDeletionQueueEntries()
       → DELETEs the stale paths from FailedRestCatalogDeletionPaths
    2. ApplyIcebergMetadataChanges()
       → same metadataPath is fetched again (REST catalog unchanged)
       → InsertDeletionQueueRecord succeeds (no duplicate since it was deleted in step 1)
   ...

Partial fix of #226 : we would still run into the same error if backend exits without executing any subsequent transaction

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Checklist

• I have tested my changes and added tests if necessary
• I updated documentation if needed
• I confirm that all my commits are signed off (DCO)