* moves configure ddp to each backend
* moves configure ddp to each backend
* moves configure ddp to each backend
* added torch manual seed in test_mean_error
* test for complicated batch structure
* test for complicated batch structure
* test for complicated batch structure
Co-authored-by: ananyahjha93 <ananya@pytorchlightning.ai>
* refactored callback system and init ddp
* refactored callback system and init ddp
* refactored callback system and init ddp
* refactored callback system and init ddp
* ref: make each backend independent for easier debugging and independent debugging
* ref: make each backend independent for easier debugging and independent debugging
* ref: make each backend independent for easier debugging and independent debugging
* ref: make each backend independent for easier debugging and independent debugging
* ref: make each backend independent for easier debugging and independent debugging
* ref: make each backend independent for easier debugging and independent debugging
* ref: test val epoch end
* ref: test val epoch end