Normalise a builder key into a WriteSigner.
A viem LocalAccount, a viem WalletClient, or a { signMessage } object (returned as-is).
LocalAccount
WalletClient
{ signMessage }
account for a wallet client without a hoisted account.
account
A signer whose signMessage produces EIP-191 signatures.
signMessage
When a wallet client has no account to sign with, or the source exposes no signMessage function.
Normalise a builder key into a WriteSigner.