add MPO.from_dense and MPO auto filling #255

Job	Run time
run-tests (matrix, base, ubuntu-latest, 3.9, false)	1m 47s
run-tests (matrix, base, ubuntu-latest, 3.10, false)	2m 6s
run-tests (matrix, base, ubuntu-latest, 3.11, false)	2m 1s
run-tests (tensor, base, ubuntu-latest, 3.9, false)	7m 29s
run-tests (tensor, base, ubuntu-latest, 3.10, false)	7m 28s
run-tests (tensor, base, ubuntu-latest, 3.11, false)	7m 29s
run-tests (macos-latest, matrix, base, 3.11, true)	2m 32s
run-tests (macos-latest, tensor, base, 3.11, false)	7m 12s
run-tests (windows-latest, matrix, base, 3.11, false)	4m 51s
run-tests (windows-latest, tensor, base, 3.11, false)	7m 19s
run-tests (torch, tensor, ubuntu-latest, 3.11, false)	7m 28s
run-tests (jax, tensor, ubuntu-latest, 3.11, false)	7m 29s
run-tests (tensorflow, tensor, ubuntu-latest, 3.11, false)	7m 28s
run-tests (slepc, matrix, ubuntu-latest, 3.11, false)	1m 59s
	1h 14m 38s

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