EVM: Add settler function to set safeguards with a signature

[alavarello]

Lets anyone submit a safeguard on a user's behalf with that user's EIP-712 signature. Previously setSafeguard took the user from msg.sender, so users had to send the tx themselves.

function setSafeguardWithSignature(                                                                                                                                                           
    address user, bytes memory safeguard, uint256 nonce, uint256 deadline, bytes memory signature                                                                                             
) external                                                                                                                                                                                    

Decisions worth review

User-chosen nonces (isUserSafeguardNonceUsed[user][nonce]), not a sequential counter. A counter forces signatures to be consumed in issue order, so one unsubmitted signature blocks
every later one. Each signature stays single-use; the deadline bounds how long an unsubmitted one lives.

ERC-1271 is supported, so Safe and other smart accounts work. ECDSA is tried first, unlike OZ's isValidSignatureNow which branches on code.length — post-Pectra an
EIP-7702-delegated EOA has code, and OZ's ordering would reject its valid ECDSA signature.

Two things integrators need to know: clients must sign through Safe's own message flow (protocol-kit), not by signing our digest directly; and an empty signature is valid for accounts
that record approved messages on-chain, so it must not be treated as a skip.

via-IR is now required, not an optimization. Every way of adding ERC-1271 overflowed EIP-170 under the legacy pipeline (24,726–24,823 vs. the 24,576 limit — externalizing the check was
the worst of them). With viaIR: true, Settler is 23,248 with 1,328 bytes spare.