Update zksync-ethers SDK to support signing smart account transactions via external signers (e.g. Metamask)

[ly0va]

With K1 signer support added to the smart account, it should be possible to sign smart account transactions via Metamask.

However, zksync-ethers SDK's class SmartAccount provides an incorrect signature for its payloadSigner hook: it accepts a hash, whereas metamask expects an unhashed message (and hence hashes it again).

This makes it impossible to use external signers such as metamask with SmartAccount class.
The task is to fix it and test if it works.

[MexicanAce]

@ly0va Unsure this is an issue for this repo. Perhaps we should move this to https://github.com/zksync-sdk/zksync-ethers ?