refactor: splitting up of NonlinearSolve #232

Job	Run time
test (Core, 1.10, ubuntu-latest)	10m 16s
test (Core, 1.10, macos-latest)	7m 33s
test (Core, 1.10, windows-latest)	14m 16s
test (Core, 1, ubuntu-latest)	16m 32s
test (Core, 1, macos-latest)	11m 18s
test (Core, 1, windows-latest)	20m 7s
test (Downstream, 1.10, ubuntu-latest)	7m 50s
test (Downstream, 1.10, macos-latest)	5m 0s
test (Downstream, 1.10, windows-latest)	11m 28s
test (Downstream, 1, ubuntu-latest)	16m 31s
test (Downstream, 1, macos-latest)	12m 50s
test (Downstream, 1, windows-latest)	20m 33s
test (Wrappers, 1.10, ubuntu-latest)	8m 44s
test (Wrappers, 1.10, macos-latest)	6m 9s
test (Wrappers, 1.10, windows-latest)	12m 9s
test (Wrappers, 1, ubuntu-latest)	16m 23s
test (Wrappers, 1, macos-latest)	11m 19s
test (Wrappers, 1, windows-latest)	20m 3s
	3h 49m 1s

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