Story: Prove the credit round trip over the corpus

Run the ORE round trip over the credit corpus at the new shape and prove that every trade survives import, export and re-import.

• Each trade in the credit corpus is imported, exported alone and imported again, and gives the same family rows.

• The proof compares the family rows of two imports, not the document text. A spelling the table does not keep, such as false for a flag, is not a difference.
• The set of known differences is empty and fails in both directions. A name that differs fails the suite, and a name listed that stops differing fails it too. An empty set is therefore a live claim, not a silence.
• The proof carries a control. The round trip passed on its first run, so each trade must render a header row and a leg row, and a control changes the recovery rate of a credit default swap and expects the rendering to change.

• The treasury lock of an agreement's underlying, which the credit corpus does not hold.

Every credit trade of Example_Trades comes back as the same family rows. The proof walks eight documents with eight trades, pins both counts, and keeps a closed set of known differences that is empty. A control shows that a changed stored field changes the rendering, and each trade must hold a header row and a leg row.

Acceptance met: the corpus test pins eight documents and eight trades, and the set of known differences is empty.