* Refactor to create abstract ParallelOpCombiner

* First draft of CombineParallelDense

* Begin to work on tests

* Test

* Refactor to move out more common code

* Clean up

* Fix

* Remove statics

* fix wording

* Start to add combine_parallel_op_batch

* Resolve PR comments

* Resolve PR comments

* dummy change to retrigger CI

* Change special case from bias_add to add

* Revert special case change

* Ignore units check

* dummy change to retrigger CI

* dummy change to re-trigger CI

* Improve docs

* Update docs

* Update docs