refactor: Enhance calendar event comparison for migration (#287)

Enhances calendar events comparison for migration by ignoring
seconds, and milliseconds improving compatibility with the new
codebase. Previously, seconds and milliseconds were not considered.
Now, both calendar events and course date blocks have seconds and
milliseconds set to zero for precise matching, ensuring a smooth
transition.

Fixes: LEARNER-9924

Author: HamzaIsrar12

course/src/main/java/org/openedx/course/presentation/calendarsync/CalendarManager.kt

@@ -294,7 +294,18 @@ class CalendarManager(
                 }
 
                 matchedDate?.let { unit ->
-                    if (unit.date.toCalendar().timeInMillis == dueDateInMillis) {
+                    val dueDateCalendar = Calendar.getInstance().apply {
+                        timeInMillis = dueDateInMillis
+                        set(Calendar.SECOND, 0)
+                        set(Calendar.MILLISECOND, 0)
+                    }
+
+                    val unitDateCalendar = unit.date.toCalendar().apply {
+                        set(Calendar.SECOND, 0)
+                        set(Calendar.MILLISECOND, 0)
+                    }
+
+                    if (dueDateCalendar == unitDateCalendar) {
                         datesList.remove(unit)
                     } else {
                         // If any single value isn't matched, return false