* fix the problems weights bug
* refactor: remove DSExpGen
* update problems weights calculation
* update problems weights calculation
* remove the selection parameter from exp_gen
* v2 support draft
* v3 also support decomposition
* make the identify_problems an independent function
* fix minor bug
* reformat
* rename exp_num to weighted_exp_num
* add the set_current_selection before the exp_gen when merging
* reformat
* fix wrong selection
* refactor: drop selection arg from ExpGen.gen and DS merge generators
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Co-authored-by: Xu <v-xuminrui@microsoft.com>
Co-authored-by: Young <afe.young@gmail.com>
Co-authored-by: Xu Yang <xuyang1@microsoft.com>