Make it easier to build with debug or int64 flags

[tdrwenski]

• don't always add -O3 flag. Instead use CMAKE_BUILD_TYPE which will also add that flag if you set the type to release (default type) and can also set debug flags.
• Update radiuss-spack-configs version to include changes I made to the Quandary spack package-- style fixes, add int64 variant that uses petsc int64 variant, use petsc debug variant when build_type=Debug

If you want to build in debug mode you can either use the spack spec quandary build_type=Debug which automatically uses petsc in debug mode, or with CMake you can do cmake -DCMAKE_BUILD_TYPE=Debug ... With spack you can also choose petsc in 64 bit int mode using quandary+int64.

[steffi7574]

Can you add those instructions somewhere, e.g. in the Readme, or in the installation section of the user guide?

//If you want to build in debug mode you can either use the spack spec quandary build_type=Debug which automatically uses petsc in debug mode, or with CMake you can do cmake -DCMAKE_BUILD_TYPE=Debug ... With spack you can also choose petsc in 64 bit int mode using quandary+int64.