Decrease Ethena ARM cross price to 0.9999

[clement-ux]

Summary

• Add mainnet governance proposal script 038_DecreaseEthenaARMCrossPriceScript.
• Call setCrossPrice(Mainnet.SUSDE, 0.9999e36) on the governance-owned Ethena ARM.
• Reproduce the required operational preparation on forks by claiming pending sUSDe redemptions and selling the remaining sUSDe balance before simulating governance.
• Update the Ethena ARM smoke-test expectation to the new cross price.

Operational requirements

Ethena ARM rejects a cross-price decrease while it still has meaningful sUSDe exposure. Before the proposal is executed on mainnet, the operator must:

1. Claim all pending sUSDe redemptions.
2. Clear the remaining sUSDe balance from the ARM.

The preparation implemented in _prepareForkState() is fork-only and does not broadcast operational transactions during real deployment.

Testing

• forge build
• Ethena ARM smoke suite: 12 passed, 0 failed
• Full smoke run: Ethena and Paxos passed; four unrelated Lido/EtherFi tests initially hit transient RPC timeouts and all passed with forge test --rerun