tests: fix msvc transient failures when sleep_ms takes longer

vlib/time/stopwatch_test.v

@@ -1,6 +1,9 @@
 import time
 
-fn test_stopwatch_works_as_intended(){
+// NB: on CI jobs, especially msvc ones, sleep_ms may sleep for much more
+// time than you have specified. To avoid false positives from CI test
+// failures, some of the asserts will be run only if you pass `-d stopwatch`
+fn test_stopwatch_works_as_intended() {
 	sw := time.new_stopwatch()
 	// sample code that you want to measure:
 	println('Hello world')
@@ -10,19 +13,23 @@ fn test_stopwatch_works_as_intended(){
 	assert sw.elapsed().nanoseconds() > 0
 }
 
-fn test_stopwatch_time_between_pause_and_start_should_be_skipped_in_elapsed(){
+fn test_stopwatch_time_between_pause_and_start_should_be_skipped_in_elapsed() {
 	sw := time.new_stopwatch()
 	time.sleep_ms(10) // A
-	//eprintln('${sw.elapsed().milliseconds()}ms')
+	// eprintln('${sw.elapsed().milliseconds()}ms')
 	assert sw.elapsed().milliseconds() >= 10
 	sw.pause()
 	time.sleep_ms(10)
-	//eprintln('${sw.elapsed().milliseconds()}ms')
+	// eprintln('${sw.elapsed().milliseconds()}ms')
 	assert sw.elapsed().milliseconds() >= 10
+	$if stopwatch {
 		assert sw.elapsed().milliseconds() < 20
+	}
 	sw.start()
 	time.sleep_ms(10) // B
-	// Here, sw.elapsed() should be ~10ms (from A) + 10ms (from B) = 20ms
+	// Here, sw.elapsed() should be ~10ms (from A) + ~10ms (from B) >= 20ms
 	assert sw.elapsed().milliseconds() >= 20
+	$if stopwatch {
 		assert sw.elapsed().milliseconds() < 30
+	}
 }