Update to math/rand/v2

This commit updates the uses of math/rand to math/rand/v2, which was
released in Go 1.22 (2024-02).

The new package is generally safer, see https://go.dev/blog/randv2 for
the details.

There are no user-visible changes, it is only adjusting the name of
functions, simplify some code thanks to v2 having a better API, etc.

chasquid.go

@@ -8,7 +8,6 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"math/rand"
 	"net"
 	"os"
 	"os/signal"
@@ -52,9 +51,6 @@ func main() {
 
 	log.Infof("chasquid starting (version %s)", version)
 
-	// Seed the PRNG, just to prevent for it to be totally predictable.
-	rand.Seed(time.Now().UnixNano())
-
 	conf, err := config.Load(*configDir+"/chasquid.conf", *configOverrides)
 	if err != nil {
 		log.Fatalf("Error loading config: %v", err)