add docstring for gate_factory, richer docstring for state_vector_bat… #114

Job	Run time
Install Python package (linux, x86_64, cpu, 3.12)	3m 18s
Install Python package (linux, x86_64, cuda, 3.12)	12m 12s
Install Library (linux, x86_64, cpu)	1m 46s
Install Python package (macos, x86_64, cpu, 3.12)	4m 11s
Install Library (linux, x86_64, cuda)	9m 56s
Install Library (macos, x86_64, cpu)	2m 39s
Install Python package (macos, arm64, cpu, 3.12)	3m 22s
Install Library (macos, arm64, cpu)	2m 34s
	39m 58s

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