Add `read_user` convenience method to `UserDatabase` base class #8

Job	Run time
unit_tests (3.8)	23s
unit_tests (3.9)	23s
unit_tests (3.10)	21s
unit_tests (3.11)	22s
unit_tests (3.12)	23s
py_build_tests / py_build_tests	8s
py_build_tests / relative_path_tests	7s
	2m 7s

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