fix type stability of SimpleNonlinearSolve (#536) #365

Job	Run time
downgrade (1.10, core)	16s
downgrade (1.10, downstream)	17s
downgrade (1.10, wrappers)	20s
test (core, 1.10, ubuntu-latest)	16m 20s
test (core, 1.10, macos-latest)	21m 35s
test (core, 1.10, windows-latest)	27m 32s
test (core, 1, ubuntu-latest)	26m 42s
test (core, 1, macos-latest)	25m 9s
test (core, 1, windows-latest)	39m 54s
test (downstream, 1.10, ubuntu-latest)	11m 9s
test (downstream, 1.10, macos-latest)	8m 7s
test (downstream, 1.10, windows-latest)	15m 11s
test (downstream, 1, ubuntu-latest)	20m 37s
test (downstream, 1, macos-latest)	14m 50s
test (downstream, 1, windows-latest)	22m 52s
test (wrappers, 1.10, ubuntu-latest)	9m 12s
test (wrappers, 1.10, macos-latest)	6m 30s
test (wrappers, 1.10, windows-latest)	11m 25s
test (wrappers, 1, ubuntu-latest)	16m 8s
test (wrappers, 1, macos-latest)	11m 43s
test (wrappers, 1, windows-latest)	19m 34s
	5h 25m 23s

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