Cassandra: TransactWriteItems writes no stream record #516

Summary

On the Cassandra backend a TransactWriteItems Put, Update or Delete on a table with an enabled stream records nothing to the stream. PutItem and BatchWriteItem on the same table record as expected; SQLite records all five shapes.

Measured on a server built from main 744ea29 against a Cassandra 4.1 node: a fresh table with NEW_AND_OLD_IMAGES, one PutItem, one BatchWriteItem Put, one TransactWriteItems with a Put, an Update and a Delete; GetRecords from TRIM_HORIZON on every shard returned the two single-item writes and none of the three transacted ones. On the service a transacted write produces a stream record like any other write.

Cause

crates/storage-cassandra/src/data/transactions.rs has no stream handling: the LOGGED BATCH it builds carries the item mutations only. The single-item and batch paths go through the write helpers that append the stream record to the batch.

Fix shape

Route the transaction's mutations through the same stream capture the single-item path uses, appending one stream record per item mutation to the LOGGED BATCH, so the record and the item land together. A wire test with a transacted Put, Update and Delete on a streamed table, run on every backend.

Found while reviewing #515.