add timeline pkg to flutter

packages/z-timeline/lib/src/services/timeline_projection_service.dart

@@ -0,0 +1,42 @@
+import '../models/timeline_entry.dart';
+import '../models/projected_entry.dart';
+import 'time_scale_service.dart';
+
+class TimelineProjectionService {
+  const TimelineProjectionService();
+
+  Map<String, List<ProjectedEntry>> project({
+    required Iterable<TimelineEntry> entries,
+    required DateTime domainStart,
+    required DateTime domainEnd,
+  }) {
+    final byGroup = <String, List<ProjectedEntry>>{};
+    for (final e in entries) {
+      if (e.overlaps(domainStart, domainEnd)) {
+        final startX = TimeScaleService.mapTimeToPosition(
+          e.start.isBefore(domainStart) ? domainStart : e.start,
+          domainStart,
+          domainEnd,
+        ).clamp(0.0, 1.0);
+        final endX = TimeScaleService.mapTimeToPosition(
+          e.end.isAfter(domainEnd) ? domainEnd : e.end,
+          domainStart,
+          domainEnd,
+        ).clamp(0.0, 1.0);
+
+        final pe = ProjectedEntry(entry: e, startX: startX, endX: endX);
+        (byGroup[e.groupId] ??= <ProjectedEntry>[]).add(pe);
+      }
+    }
+
+    // Keep original order stable by lane then startX
+    for (final list in byGroup.values) {
+      list.sort((a, b) {
+        final laneCmp = a.entry.lane.compareTo(b.entry.lane);
+        if (laneCmp != 0) return laneCmp;
+        return a.startX.compareTo(b.startX);
+      });
+    }
+    return byGroup;
+  }
+}