SMP futures: the rules (perpetuals on market prices, house = insurance fund)

Not wired into the game yet: the glue waits for the market's mark_price/twap/volume API.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

native/smp/src/lib.rs

@@ -21,6 +21,8 @@ pub mod smp_casino_slots;
 pub mod smp_claims;
 #[path = "../mixins/smp/smp_economy.rs"]
 pub mod smp_economy;
+#[path = "../mixins/smp/smp_futures.rs"]
+pub mod smp_futures;
 #[path = "../mixins/smp/smp_games.rs"]
 pub mod smp_games;
 #[path = "../mixins/smp/smp_invsee.rs"]