Fix Viem upstream: transaction serializers should support async

[CedarMist]

As per: wevm/viem#2696

Tried to fix upstream

[CedarMist]

A suggestion was made on how to implement this cleanly with Viem:

import {
  keccak256,
  serializeTransaction,
  type TransactionSerializable,
  type Hex,
  type Signature,
} from "viem";
import { sign, privateKeyToAccount, toAccount } from "viem/accounts";

async function serializerAsync(
  transaction: TransactionSerializable,
  signature?: Signature | undefined,
): Promise<Hex> {
  // ... perform async operations
  return serializeTransaction(transaction, signature);
}

const privateKey = "0x..." as const;

const account = toAccount({
  ...privateKeyToAccount(privateKey),
  async signTransaction(transaction) {
    const signature = await sign({
      hash: keccak256(await serializerAsync(transaction)),
      privateKey,
    });
    return serializerAsync(transaction, signature);
  },
});

Currently the Viem integration has a workaround to fetch the calldata public keys in the background because the transaction serializer isn't async:

sapphire-paratime/integrations/viem-v2/src/index.ts

Lines 125 to 134 in f708f39

	const fetcher = new KeyFetcher();
	const provider = client as EthereumProvider;
	await fetcher.fetch(provider);
	// The fetcher runs in the background, routinely fetching the keys
	// This means when the serializer requests a calldata public key one will
	// have been retrieved pre-emptively.
	const intervalId: NodeJS.Timeout | number = setInterval(async () => {
	await fetcher.fetch(provider);
	}, fetcher.timeoutMilliseconds);

However, this isn't ideal.

There are other sore-spots in the Viem & Wagmi integrations:

• Wagmi supports support EIP-6963 via the MIPD package: https://github.com/wevm/mipd
  • Couldn't figure out a clean way of auto-wrapping via MIPD, so eth_call and eth_estimateGas wouldn't be encrypted as they aren't wrapped.
• TBD: remember more

Overall, we can't just focus on Viem, need to make sure it works well with Wagmi in the way people commonly use it, and with the third-party RPC providers & SDKs like WalletConnect & RainbowKit