mpi: Drop dual mode and tweak overlap2/full modes for GPU backends #456

Job	Run time
pytest-docker-py310-gcc-omp-arm64-base	33m 38s
pytest-docker-py310-icx-omp-adjoint	30m 54s
pytest-ubuntu-py310-gcc14-omp-base	49m 17s
pytest-docker-py310-gcc-omp-arm64-adjoint	26m 12s
pytest-docker-py310-gcc-omp-adjoint	30m 26s
pytest-docker-py310-gcc-omp-base	36m 58s
pytest-ubuntu-py311-gcc10-noomp-adjoint	33m 42s
pytest-ubuntu-py310-gcc9-omp-adjoint	36m 26s
pytest-ubuntu-py313-gcc14-omp-base	39m 2s
pytest-ubuntu-py312-gcc13-omp-base	53m 13s
pytest-ubuntu-py313-gcc14-omp-adjoint	40m 16s
pytest-ubuntu-py311-gcc11-cxxnoomp-base	49m 2s
pytest-ubuntu-py311-gcc10-noomp-base	45m 25s
pytest-docker-py310-icx-omp-base	39m 33s
pytest-ubuntu-py310-gcc9-omp-base	46m 25s
pytest-ubuntu-py312-gcc12-cxxomp-adjoint	41m 19s
pytest-ubuntu-py311-gcc11-cxxnoomp-adjoint	26m 58s
pytest-osx-py312-clang-omp-base	36m 42s
pytest-ubuntu-py312-gcc13-omp-adjoint	40m 36s
pytest-ubuntu-py310-gcc14-omp-adjoint	27m 25s
pytest-ubuntu-py312-gcc12-cxxomp-base	57m 37s
	13h 41m 6s

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