pub fn get(&self, key: KeySlice) -> Option<Bytes> {
        let key_bytes = KeyBytes::from_bytes_with_ts(
            Bytes::from_static(unsafe { std::mem::transmute::<&[u8], &[u8]>(key.key_ref()) }),
            key.ts(),
        );
        self.map.get(&key_bytes).map(|e| e.value().clone())
    }
Get a value by key. Should not be used in week 3.
mini-lsm-mvcc/src/mem_table.rs