MuonLayerHoughTool memory leak fixes & improvements
- Clean up pointers in HoughDataPerSec destructor to prevent possible memory leak
- Clean up tgcClusteringObjs in MuonLayerHoughTool::State destructor
- Avoid inheriting from std::vector
- Some style changes and documentation that make variable usage and memory management more obvious to the reader
@wleight Unfortunately, I still haven't managed to run Valgrind locally to confirm the fixes due to insufficient resources, and running on lxplus is slow and unreliable (getting kicked off halfway the run). I am proposing to merge the changes (if they pass CI) and then see if the leaks still pop up in the regular Valgrind tests done by the SPOT group. I know this isn't ideal, but it's a way forward at least. The fixes are also just general improvements, and I don't expect they'll make things worse, in any case.