* Implement saving stats as an EVLR
* Fix layout tests
* don't save statistics unless copc was generated by pdal
* Address Martin reviews
* Address reviews
* Only read stats EVLR and do not store count
* merge cleanup
* Address reviews
- Remove waiting for task to finish in ~QgsPointCloudLayer
- Fix failing ept provider test when maximum threads is set to 1.
- make PointCloudStatisticsCalculationState into enum class
- move AttributeStatistics outside QgsPointCloudStatistics