fix: Add hit count in root dump reader (#3929)

Adds hit count information to particles read from the `RootAthenaDumpReader`. Even though simhits != measurements strictely speaking, in that scenario it is ok to assume this I think.

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
	- Enhanced particle measurement tracking by updating the `newParticle` object to accurately reflect the number of hits during processing.

- **Bug Fixes**
	- Improved accuracy in the processing of particles by ensuring the number of hits is correctly determined.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Examples/Io/Root/src/RootAthenaDumpReader.cpp

@@ -672,6 +672,7 @@ RootAthenaDumpReader::reprocessParticles(
     }
 
     auto newParticle = particle.withParticleId(fatrasBarcode);
+    newParticle.final().setNumberOfHits(std::distance(begin, end));
     newParticles.push_back(newParticle);
 
     for (auto it = begin; it != end; ++it) {