Implement slog.LogValuer #107

type customError struct {
 ...
}
func (e customError) Error() string {
 ...
}
// implements slog.LogValuer
func (e customError) LogValue() slog.Value {
	return slog.GroupValue(
	 slog.Int("code", e.code),
	 slog.String("message", e.msg),
	 slog.String("stacktrace", e.stacktrace),
 )
}