* iceberg: support multi-table transaction commit
Add handleCommitTransaction for POST /v1/transactions/commit. Validation
is atomic across all table-changes (resolve, load, evaluate every
requirement before any write); metadata writes and pointer flips are
best-effort with rollback, so this is not crash-atomic.
* iceberg: route transactions/commit with and without prefix
* iceberg: test transaction commit request decoding
* iceberg: restore full prior table state on transaction rollback
* iceberg: test transaction rollback restores full prior table state
* iceberg: only clean up metadata for rolled-back tables
Chris Lu
1ca628d3e9