Add validation to `@ChainKey` to prevent utf 0 in keys

suggested changes:

```diff
export interface ChainKeyMetadata extends ChainKeyConfig {
key: string | symbol;
+ allowUtf0?: boolean
}

export function ChainKey(chainKeyConfig: ChainKeyConfig): PropertyDecorator {
return (target, key) => {
const fields: ChainKeyMetadata[] = Reflect.getOwnMetadata("galachain:chainkey", target) || [];

const existingField = fields.find((field) => field.position === chainKeyConfig.position);

+ // inject somewhere a validation decotator to fail on utf0

if (existingField === undefined) {
fields.push({ key, ...chainKeyConfig });
Reflect.defineMetadata("galachain:chainkey", fields, target);
}
};
}
```