Add Halley's method via descent API #147

Job	Run time
downgrade (1.10, core)	11m 25s
downgrade (1.10, adjoint)	8m 44s
downgrade (1.10, alloc_check)	8m 33s
test (1.10, ubuntu-latest, core)	11m 14s
test (1.10, ubuntu-latest, adjoint)	8m 33s
test (1.10, ubuntu-latest, alloc_check)	8m 33s
test (1.10, macos-latest, core)	7m 1s
test (1.10, macos-latest, adjoint)	6m 20s
test (1.10, macos-latest, alloc_check)	6m 8s
test (1.10, windows-latest, core)	12m 36s
test (1.10, windows-latest, adjoint)	10m 10s
test (1.10, windows-latest, alloc_check)	10m 16s
test (1, ubuntu-latest, core)	21m 25s
test (1, ubuntu-latest, adjoint)	15m 41s
test (1, ubuntu-latest, alloc_check)	14m 56s
test (1, macos-latest, core)	11m 33s
test (1, macos-latest, adjoint)	10m 17s
test (1, macos-latest, alloc_check)	10m 42s
test (1, windows-latest, core)	20m 14s
test (1, windows-latest, adjoint)	17m 48s
test (1, windows-latest, alloc_check)	16m 18s
	4h 8m 27s

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