Implement slog.LogValuer

[samber]

The new slog library provides a slog.LogValuer interface for formatting attributes.

Documentation here: https://pkg.go.dev/golang.org/x/exp/slog#hdr-Customizing_a_type_s_logging_behavior

I think palantir/stacktrace should implement it.

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),
        )
}

slog will be released in go 1.21. But is already available and golang.org/x/exp/slog