SIMD-0529: big_integer mod_exp syscall

Not active on mainnet-beta; not active on testnet; not active on devnet.

Introduced in anza-xyz/agave PR #16585.

Feature id expHkkpN92z71GU7EwB7AXCy8Mz4kzDJFpGY1dZV9A7.

Related

Vortex Testnet