pkg: use modern Go stdlib functions to simplify code (#5209)

- strings.CutPrefix instead of HasPrefix+TrimPrefix (naming, legacy)
- slices.Contains instead of manual loop (plugin/server)
- min/max builtins instead of manual comparisons (nathole)

pkg/naming/names.go

@@ -16,9 +16,8 @@ func StripUserPrefix(user, name string) string {
 	if user == "" {
 		return name
 	}
-	prefix := user + "."
-	if strings.HasPrefix(name, prefix) {
-		return strings.TrimPrefix(name, prefix)
+	if trimmed, ok := strings.CutPrefix(name, user+"."); ok {
+		return trimmed
 	}
 	return name
 }