add support for network calculation from the calculator

lib/components/pages/loco_timeline/timeline_grid.dart

@@ -813,17 +813,17 @@ List<DateTime> _buildBoundaries(
   for (final seg in segments) {
     boundaryDates.add(seg.start);
     boundaryDates.add(seg.end);
-    minStart = minStart == null || seg.start.isBefore(minStart!)
+    minStart = minStart == null || seg.start.isBefore(minStart)
         ? seg.start
         : minStart;
-    maxEnd = maxEnd == null || seg.end.isAfter(maxEnd!) ? seg.end : maxEnd;
+    maxEnd = maxEnd == null || seg.end.isAfter(maxEnd) ? seg.end : maxEnd;
   }
-  minStart ??= now.subtract(const Duration(days: 1));
+  final effectiveMinStart = minStart ?? now.subtract(const Duration(days: 1));
   final effectiveMaxEnd = maxEnd ?? now;
   boundaryDates.add(effectiveMaxEnd);
   var boundaries = boundaryDates.toList()..sort();
   if (boundaries.length < 2) {
-    boundaries = [minStart!, effectiveMaxEnd];
+    boundaries = [effectiveMinStart, effectiveMaxEnd];
   }
   return boundaries;
 }