db/select-* to toucan 2 (#29319)

* db/select-one-field -> t2/select-one-fn

* `db/select-field` -> `t2/select-fn-set`

* db/select-ids -> t2/select-pk-set

* db/select-field->field -> t2/select-fn->fn

* db/select-field->id -> t2/select-fn->pk

* `db/select-id->field` -> `t2/select-pk->field`

* add discourage var