Fix MIDI timestamp handling in FourOscPlugin for sample-accurate timing

The FourOscPlugin had a timing bug where MIDI timestamps (in seconds)
were incorrectly cast to integers and treated as sample positions.
This caused all MIDI events to be shifted toward the beginning of audio blocks,
reducing timing accuracy.
Changes:
- Convert timestamps from seconds to samples using getSampleRate()
- Use roundToInt() for proper rounding instead of truncation
Impact:
- Fixes sample-accurate MIDI timing for synthesizer voice triggering

Author: ruguevara

modules/tracktion_engine/plugins/effects/tracktion_FourOscPlugin.cpp

@@ -1487,7 +1487,7 @@ void FourOscPlugin::applyToBuffer (const PluginRenderContext& fc)
             {
                 for (auto m : *fc.bufferForMidiMessages)
                 {
-                    int midiPos = int (m.getTimeStamp());
+                    int midiPos = juce::roundToInt (m.getTimeStamp() * getSampleRate());
                     if (midiPos >= pos && midiPos < pos + thisBlock)
                         midi.addEvent (m, midiPos - pos);
                 }