Slope limiter pass by reference #1364

Job	Run time
build_libraries_appleM1	2m 5s
build_libraries	2m 7s
build_libraries_riscv	1m 3s
build_testpackage	2m 5s
build_tools	55s
build_riscv	0s
build_appleM1	2m 41s
build_production_1st_order_space	3m 26s
build_ionosphereTests	1m 30s
build_production	3m 31s
build_production_1st_order_time	3m 34s
run_testpackage	45m 3s
run_ionosphere_LFMtest	1m 16s
check_cfg_files	1m 6s
	1h 10m 22s

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