Prefer strconv over fmt

When converting primitives to/from strings, strconv is faster thanfmt.

BadGood
  1. for i := 0; i < b.N; i++ {
  2.   s := fmt.Sprint(rand.Int())
  3. }
 
  1. for i := 0; i < b.N; i++ {
  2.   s := strconv.Itoa(rand.Int())
  3. }
  1. BenchmarkFmtSprint-4    143 ns/op    2 allocs/op
 
  1. BenchmarkStrconv-4    64.2 ns/op    1 allocs/op