fix(examples) import 'u'-prefixed versions of modules (#2365)

import usys and utime instead of sys and time, as the latter are not available on all platforms

examples/widgets/roller/lv_example_roller_3.py

@@ -1,8 +1,8 @@
 #!/opt/bin/lv_micropython -i
-import time
+import utime as time
 import lvgl as lv
 import display_driver
-import sys
+import usys as sys
 
 class Lv_Roller_3():