refactor DecodeEventRecord

[failfmi]

DecodeEventRecord must take a DecodeEvent from the specific module.
https://github.com/LimeChain/gosemble/blob/develop/primitives/types/event.go#L46

[radkomih]

Events:             support.NewHashStorageValue(keySystem, keyEvents, func(*bytes.Buffer) (types.EventRecord, error) { return types.EventRecord{}, nil })

If anyone calls the Get() method on this storage item, it will invoke the DecodeEventRecord which does nothing (there are separate decoding functions for each event type). Most probably, it won't happen at runtime, however, at least we should log something or modify the method to ensure that the user is aware of this.