refactor!: move preconditioners inside linear solvers #253

Job	Run time
downgrade (1.10, core)	16m 9s
test (core, 1.10, ubuntu-latest)	15m 49s
test (core, 1.10, macos-latest)	12m 15s
test (core, 1.10, windows-latest)	19m 51s
downgrade (1.10, downstream)	8m 37s
test (core, 1, ubuntu-latest)	21m 50s
downgrade (1.10, wrappers)	10m 11s
test (core, 1, macos-latest)	15m 19s
test (core, 1, windows-latest)	21m 46s
test (downstream, 1.10, ubuntu-latest)	8m 0s
test (downstream, 1.10, macos-latest)	5m 35s
test (downstream, 1.10, windows-latest)	11m 9s
test (downstream, 1, ubuntu-latest)	17m 17s
test (downstream, 1, macos-latest)	7m 39s
test (downstream, 1, windows-latest)	21m 36s
test (wrappers, 1.10, ubuntu-latest)	10m 2s
test (wrappers, 1.10, macos-latest)	4m 52s
test (wrappers, 1.10, windows-latest)	12m 51s
test (wrappers, 1, ubuntu-latest)	19m 9s
test (wrappers, 1, macos-latest)	4m 11s
test (wrappers, 1, windows-latest)	21m 43s
	4h 45m 51s

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