refactor: splitting up of NonlinearSolve #204

Job	Run time
test (Core, min, ubuntu-latest)	48m 26s
test (Core, min, macos-latest)	32m 20s
test (Core, min, windows-latest)	55m 25s
test (Core, 1, ubuntu-latest)	14m 25s
test (Core, 1, macos-latest)	8m 55s
test (Core, 1, windows-latest)	17m 28s
test (Downstream, min, ubuntu-latest)	7m 54s
test (Downstream, min, macos-latest)	5m 8s
test (Downstream, min, windows-latest)	11m 3s
test (Downstream, 1, ubuntu-latest)	14m 12s
test (Downstream, 1, macos-latest)	8m 30s
test (Downstream, 1, windows-latest)	17m 2s
test (Misc, min, ubuntu-latest)	10m 40s
test (Misc, min, macos-latest)	6m 11s
test (Misc, min, windows-latest)	14m 39s
test (Misc, 1, ubuntu-latest)	14m 1s
test (Misc, 1, macos-latest)	9m 15s
test (Misc, 1, windows-latest)	17m 7s
test (Wrappers, min, ubuntu-latest)	9m 4s
test (Wrappers, min, macos-latest)	5m 49s
test (Wrappers, min, windows-latest)	11m 53s
test (Wrappers, 1, ubuntu-latest)	13m 58s
test (Wrappers, 1, macos-latest)	8m 41s
test (Wrappers, 1, windows-latest)	16m 48s
	6h 18m 54s

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