feat: expose error signature utils

[0xpolarzero]

abitype exposes utils for converting ABI items, e.g. functions or events, to signatures. This is not the case for errors (AbiError), although the underlying logic is present and only needs a wrapper with the right type.

We already have:

• toEventSignature / toFunctionSignature -> toSignature;
• toEventSelector / toFunctionSelector -> toSignatureHash;
• toEventHash / toFunctionHash -> toSignatureHash.

Similarily, abitype could expose some new:

• toErrorSignature -> toSignature;
• toErrorSelector -> toSignatureHash;
• toErrorHash -> toSignatureHash.

[0xpolarzero]

Wrong place, all of this is viem.