Repair CI

[stanbot8]

Restore the repository's supported CI build configurations.

• CMake cache filtering parsed unquoted values and tested a variable name for the NOTFOUND marker. Retain only defined cache values by quoting names and expanded values. CMakeLists.txt: 809-810
• CI jobs selected the system Python runtime but left pyenv setup enabled. Pass NOPYENV so CMake uses the system Python3 interpreter. .github/workflows/ci.yml
• CMake required Python 3.9 even when CI provided another supported Python3 release. Select the active Python3 interpreter through CMake's standard package discovery. CMakeLists.txt: 223
• The ParaView job omitted Qt5 development files and constructed generated-code include paths from its minimum supported ParaView release. Install Qt5 and source the active include directories from ParaView::Catalyst. CMakeLists.txt: 407-409
• Test object compilation could start while the GoogleTest external project was still extracting its headers. Add an explicit GoogleTest dependency to every generated test executable. cmake/Testing.cmake