Refund CTX to Smart Contract that issued CTX

[PropzSaladaz]

Description

Smart Contract (SC) that calls submitCTX() & funds the ephemeral account created (will have .to field set to this SC address) should receive the refund from the CTX execution:

• remaining gas from onDecrypt() execution should be moved into ctx.to.balance
• ephemeral account responsible for onDecrypt() call should be cleaned both in balance (moved into SC balance) and in nonce to clean up state usage
• Responsibility of tracking user - CTX correspondence, and its respective refund is left to SC developer. Protocol side only enforces the refund goes back to SC.