Include ERC20 decimals in useBalance result

[shrugs]

any time someone is fetching a useBalance of a token, they almost certainly also want decimals in order to format value correctly. wagmi includes symbol, which is excellent, but it would make sense to also include a fetch for decimals in this request so users don't need to construct their own erc20 contract instance and fetch it themselves

[tmm]

Good idea! #122