如何在不指定精度的情况下将big.Rat转换为字符串？

import (
    "fmt"
    "math/big"
)

func main() {
    rat := new(big.Rat)
    rat.SetFloat64(3.14159265358979323846264338327950288419716939937510582097494459)

    str := rat.FloatString(0)
    fmt.Println(str)
}

314159265358979323846264338327950288419716939937510582097494459