Market-hours risk flags

Tokenized equity markets close. The tokens never do. An agent trading a tokenized stock on Saturday is quoting Friday's price into an empty book, and the oracle is not stale by its own definition — it is reporting the last real close, which is what it is for.

`market_open` appears on every RWA result, and a session penalty is applied to the walked slippage when the underlying venue is shut. The flag stays visible so you can strip the penalty back out and reason about the raw ladder yourself.

Weekend collateral is the sharpest case: a liquidation path running through an absent book, on a position that stays fully liquidatable the whole time.