Send app_data through the solana auction

[squadgazzz]

Description

app_data is an input to the on-chain intent hash, and that hash is the order uid and the order PDA seed. The settlement encoding in #4779 has to rebuild the exact intent, but the value stopped at the database: the indexer writes solana.orders.app_data and nothing read it. This sends it through the auction so the driver can drop its zero placeholder.

Stacked on #4787 (only for the trivial conflict in the db test helpers, retarget to main once it merges).

Changes

• AppData newtype in chain-types, 0x-hex on the wire like the uid
• autopilot-svm reads app_data in open_orders and carries it on the domain order
• /solve request order gains an appData field

How to test

Updated unit tests, the wire-format pin covers the new field. The driver ignores unknown fields, so this ships independently of #4779 consuming it.

[squadgazzz]

in favor of #4780