* [WIP] abstract-data-structure

* update docs

* update

* update BaseDataSample

* fix comment and coverage 100%

* update and add _set_field

* update

* split  into base_data_element and base_data_sample

* update

* update

* update

* fix typo

* add unit tests of data abstract interface

* update

* update

* update docs of data element

* a draft of UT of datasample, to be finished

* update datasample test

* updata

* update

* fix comments

* fix comments

* fix comments

Co-authored-by: liukuikun <liukuikun@sensetime.com>