refactor: modernize Go with strings.SplitSeq and maps.Copy

Replace strings.Split loops with strings.SplitSeq iterators in the CSV
parsers (reality_scan and the scale-test helpers) and swap a manual map
copy for maps.Copy in the MTProto traffic collector. No behavior change;
these are the fixes the modernize analyzer reports.

internal/web/job/check_client_ip_scale_test.go

@@ -51,7 +51,7 @@ func scaleJobSizes(t *testing.T, def ...int) []int {
 		return def
 	}
 	var out []int
-	for _, part := range strings.Split(raw, ",") {
+	for part := range strings.SplitSeq(raw, ",") {
 		part = strings.TrimSpace(part)
 		if part == "" {
 			continue

internal/web/service/reality_scan.go

@@ -286,7 +286,7 @@ func (s *ServerService) ScanRealityTarget(target string) (*RealityScanResult, er
 
 func (s *ServerService) ScanRealityTargets(targetsCSV string) ([]*RealityScanResult, error) {
 	var tokens []string
-	for _, raw := range strings.Split(targetsCSV, ",") {
+	for raw := range strings.SplitSeq(targetsCSV, ",") {
 		if t := strings.TrimSpace(raw); t != "" {
 			tokens = append(tokens, t)
 		}

internal/web/service/scale_helpers_test.go

@@ -60,7 +60,7 @@ func scaleSizes(t *testing.T, def ...int) []int {
 		return def
 	}
 	var out []int
-	for _, part := range strings.Split(raw, ",") {
+	for part := range strings.SplitSeq(raw, ",") {
 		part = strings.TrimSpace(part)
 		if part == "" {
 			continue