[Nested Safe] Gasless signing

[katspaugh]

When Safe owns a Safe, it should be able to sign messages offchain w/o paying gas. This includes signing Safe transactions.

• adjust the “if” that redirects all smart contract wallets from signatures to onchain txs
• create a different Signature type for those sigs. 1271 Signatures a differently encoded using the static and dynamic part. But the core sdk supports this so we do not need to handle the complicated logic.