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* add key abstraction and prepare for MVCC Signed-off-by: Alex Chi <iskyzh@gmail.com> * a little bit type exercise Signed-off-by: Alex Chi <iskyzh@gmail.com> * refactor tests Signed-off-by: Alex Chi <iskyzh@gmail.com> * fix clippy warnings Signed-off-by: Alex Chi <iskyzh@gmail.com> * refactor starter code Signed-off-by: Alex Chi <iskyzh@gmail.com> * final touch docs Signed-off-by: Alex Chi <iskyzh@gmail.com> --------- Signed-off-by: Alex Chi <iskyzh@gmail.com>