AminoConverters may need to be class with prefix

- [ ] research `prefix` below

https://github.com/cosmos/cosmjs/blob/fb5cc27c3b53b8b4c8e1e003bb8b01c103b47bb9/packages/stargate/src/modules/staking/aminomessages.ts#L185-L190

https://github.com/cosmos/cosmjs/blob/fb5cc27c3b53b8b4c8e1e003bb8b01c103b47bb9/packages/stargate/src/modules/staking/aminomessages.ts#L122-L123

```js
function toAmino() {
return {
pubkey: {
typeUrl: "/cosmos.crypto.secp256k1.PubKey",
value: fromBase64(decodeBech32Pubkey(pubkey).value),
}
}

}

function fromAmino() {
return {
pubkey: encodeBech32Pubkey(
{
type: "tendermint/PubKeySecp256k1",
value: toBase64(pubkey.value),
},
prefix,
)
}
}
```