Fix LightTestStage and LightTestPipeline

- NamedString is used to register shader include files, but although the path is right, the includes do not work
- There are a lot of memory leaks in this class which can be easily solved by using unique_ptr

Locate LightTestStage and LightTestPipeline and inspect how NamedString registers shader include files. Reproduce the failed includes, then trace ownership in both classes to identify the reported leaks. Done means shader includes work despite the existing path and the class-owned allocations are released safely.

Written by the indexing model from the issue text.