Implement MatchType in TimeseriesRef for precise data retrieval

- Added an enumeration MatchType with options Exact and Nearest.
- Modified atTime and getRawIndexAtTime in TimeseriesRef to support MatchType, allowing callers to specify whether they need an exact timestamp match or the nearest available match.
- Adjusted the atTime method to throw an error when an exact match is required but not found, enhancing error handling for strict match requirements.

plotjuggler_base/include/PlotJuggler/reactive_function.h

@@ -25,7 +25,7 @@ struct TimeseriesRef
 
   void set(unsigned index, double x, double y);
 
-  double atTime(double t) const;
+  double atTime(double t, MatchType match_type) const;
 
   int getRawIndexAtTime(double t) const;
 
@@ -63,6 +63,11 @@ struct CreatedSeriesXY : public CreatedSeriesBase
   CreatedSeriesXY(PlotDataMapRef* data_map, const std::string& name);
 };
 
+enum class MatchType {
+    Exact,    // Returns an index only if the exact time is found
+    Nearest   // Returns the nearest time index (current behavior)
+};
+
 //-----------------------
 
 class ReactiveLuaFunction : public PJ::TransformFunction

plotjuggler_base/src/reactive_function.cpp

@@ -185,15 +185,34 @@ void TimeseriesRef::set(unsigned index, double x, double y)
   p = { x, y };
 }
 
-double TimeseriesRef::atTime(double t) const
+double TimeseriesRef::atTime(double t, MatchType match_type) const
 {
-  int i = _plot_data->getIndexFromX(t);
-  return _plot_data->at(i).y;
+  auto index = getRawIndexAtTime(t, match_type);
+  if (!index)
+  {
+    throw std::runtime_error("Time point not found for exact match requirement");
+  }
+  return _plot_data->at(*index).y;
 }
 
-int TimeseriesRef::getRawIndexAtTime(double t) const
+std::optional<unsigned> TimeseriesRef::getRawIndexAtTime(double t, MatchType match_type) const
 {
-  return _plot_data->getIndexFromX(t);
+  if (match_type == MatchType::Exact)
+  {
+    auto it = std::find_if(
+        _plot_data->begin(),
+        _plot_data->end(),
+        [t](const auto& point) { return point.x == t; });
+    if (it != _plot_data->end())
+    {
+      return std::distance(_plot_data->begin(), it);
+    }
+    return std::nullopt; // Exact time not found
+  }
+  else
+  {
+    return _plot_data->getIndexFromX(t); // Nearest match
+  }
 }
 
 unsigned TimeseriesRef::size() const