Parallelizes `MDAnalysis.analysis.msd` #6559

Job	Run time
sdist_check_and_build	8m 48s
build_docs	4m 19s
main_tests (ubuntu-latest, 3.10, true, true)	25m 12s
main_tests (ubuntu-latest, 3.11, true, true)	24m 53s
main_tests (ubuntu-latest, 3.12, true, true)	36m 51s
main_tests (ubuntu-latest, 3.13, false, true, python_313)	13m 19s
main_tests (macos-13, 3.12, true, true, macOS_monterey_py311)	56m 53s
main_tests (macOS-14, 3.12, false, true, macOS_14_arm64_py312)	9m 39s
main_tests (ubuntu-latest, 3.10, false, true, numpy_min, numpy=1.23.2)	14m 5s
main_tests (ubuntu-latest, 3.10, true, false, asv_check, asv)	2m 50s
	3h 16m 49s

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