Data points that match the exact maximum value set for the axis are not displayed

I've noticed an issue where data points that match the exact maximum value set for the Y axis are not displayed in the plot. To address this, I've added a fixed offset to both the minimum and maximum values when calling ImPlot::SetupAxisLimits():
```C++
constexpr double Offset = 0.5; // in order to draw values that exactly equal to min or max
ImPlot::SetupAxisLimits(ImAxis_Y1, 0.0 - Offset, currentPlot.plotMaxValue + Offset, ImGuiCond_Always);
```

While that works most of the time(for small values like %), I've observed that the issue still persists sometimes, particularly when dealing with very high maximum values.

One way obvious is to switch from a _fixed_ offset to a _percentage-based_ offset instead. But I'm wondering whether this is the best solution.

Any advice would be appreciated!

Thanks,
Yiran