feat(shuffle)!: add Shuffle and ShuffleSlice functions (#11)

Add equivalent to `Shuffle` function from `math/rand` and `math/rand/v2`
packages, but based on randomness from `crypto/rand` package. This
allows cryptographically secure shuffling of data.

Also add `ShuffleSlice` function that shuffles a slice of any type.

BREAKING CHANGE: Minimum required Go version is now 1.18 due the `ShuffleSlice` using generics.

shuffle_example_test.go

@@ -0,0 +1,32 @@
+package rands_test
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/jimeh/rands"
+)
+
+func ExampleShuffle() {
+	numbers := []int{1, 2, 3, 4, 5}
+
+	err := rands.Shuffle(len(numbers), func(i, j int) {
+		numbers[i], numbers[j] = numbers[j], numbers[i]
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(numbers) // => [2 4 5 1 3]
+}
+
+func ExampleShuffleSlice() {
+	mixed := []any{1, "two", 3.14, true, nil}
+
+	err := rands.ShuffleSlice(mixed)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(mixed) // => [3.14 true 1 two <nil>]
+}