refactor!: move preconditioners inside linear solvers #251

Job	Run time
downgrade (1.10, core)	16m 0s
downgrade (1.10, downstream)	8m 37s
downgrade (1.10, wrappers)	10m 12s
test (core, 1.10, ubuntu-latest)	15m 24s
test (core, 1.10, macos-latest)	12m 43s
test (core, 1.10, windows-latest)	21m 6s
test (core, 1, ubuntu-latest)	28m 13s
test (core, 1, macos-latest)	23m 30s
test (core, 1, windows-latest)	32m 7s
test (downstream, 1.10, ubuntu-latest)	8m 4s
test (downstream, 1.10, macos-latest)	8m 5s
test (downstream, 1.10, windows-latest)	11m 12s
test (downstream, 1, ubuntu-latest)	17m 53s
test (downstream, 1, macos-latest)	10m 52s
test (downstream, 1, windows-latest)	21m 2s
test (wrappers, 1.10, ubuntu-latest)	9m 34s
test (wrappers, 1.10, macos-latest)	8m 30s
test (wrappers, 1.10, windows-latest)	13m 8s
test (wrappers, 1, ubuntu-latest)	20m 11s
test (wrappers, 1, macos-latest)	13m 29s
test (wrappers, 1, windows-latest)	21m 46s
	5h 31m 38s

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