Nexus: Add GCTA docs and update examples #7460

Job	Run time
linux (GCC9-NoMPI-Debug-Real)	16m 26s
macos (macOS-GCC14-NoMPI-Real)	16m 11s
linux (GCC9-NoMPI-NoOMP-Real)	15m 23s
spack-centos-stream (GCC11-NoMPI-Debug-Real)	19m 32s
linux (GCC9-NoMPI-NoOMP-Complex)	15m 17s
spack-centos-stream (GCC11-NoMPI-NoOMP-Real)	17m 46s
linux (GCC9-MPI-Sandbox-Real)	3m 38s
linux (GCC9-NoMPI-Sandbox-Complex)	3m 55s
spack-centos-stream (GCC11-NoMPI-NoOMP-Complex)	18m 8s
spack-centos-stream (GCC11-NoMPI-Sandbox-Real)	4m 13s
linux (GCC9-MPI-Gcov-Real)	26m 3s
linux (GCC9-MPI-Gcov-Complex)	26m 15s
linux (GCC12-NoMPI-Werror-Real)	18m 54s
linux (GCC12-NoMPI-Werror-Complex)	19m 9s
linux (GCC12-NoMPI-Werror-Real-Mixed)	17m 55s
linux (GCC12-NoMPI-Werror-Complex-Mixed)	18m 33s
linux (Clang14-NoMPI-ASan-Real)	24m 53s
linux (Clang14-NoMPI-ASan-Complex)	24m 54s
linux (Clang14-NoMPI-UBSan-Real)	24m 9s
linux (Clang16-NoMPI-Offload-Real)	22m 52s
linux (Clang16-NoMPI-Offload-Complex)	23m 1s
	6h 17m 7s

Provide feedback