uses UTC dates as an attempt to fix heat-map's rendering bug. (#304)

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## Description

Uses UTC dates as an attempt to fix heatmap's rendering bug 

## Type of Change

<!--- Put an `x` in all the boxes that apply: -->

- [ ] ✨ New feature (non-breaking change which adds functionality)
- [x] 🛠️ Bug fix (non-breaking change which fixes an issue)
- [ ] ❌ Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] 🧹 Code refactor
- [ ] ✅ Build configuration change
- [ ] 📝 Documentation
- [ ] 🗑️ Chore

lib/pages/analytics/models/occupancy_heat_map_model.dart

@@ -21,11 +21,11 @@ class OccupancyHeatMapModel extends Equatable {
 
     return OccupancyHeatMapModel(
       uuid: json['uuid'] as String? ?? '',
-      eventDate: DateTime(
+      eventDate: DateTime.utc(
         int.parse(year ?? '2025'),
         int.parse(month ?? '1'),
         int.parse(day ?? '1'),
-      ).toUtc(),
+      ),
       countTotalPresenceDetected: num.parse(
         json['count_total_presence_detected']?.toString() ?? '0',
       ).toInt(),

lib/pages/analytics/modules/occupancy/widgets/occupancy_heat_map.dart

@@ -20,14 +20,14 @@ class OccupancyHeatMap extends StatelessWidget {
       : 0;
 
   DateTime _getStartingDate() {
-    final jan1 = DateTime(DateTime.now().year, 1, 1).toUtc();
+    final jan1 = DateTime.utc(DateTime.now().year, 1, 1);
     final startOfWeek = jan1.subtract(Duration(days: jan1.weekday - 1));
     return startOfWeek;
   }
 
   List<OccupancyPaintItem> _generatePaintItems(DateTime startDate) {
     return List.generate(_totalWeeks * 7, (index) {
-      final date = startDate.toUtc().add(Duration(days: index));
+      final date = startDate.add(Duration(days: index));
       final value = heatMapData[date] ?? 0;
       return OccupancyPaintItem(index: index, value: value, date: date);
     });