🚨 Separate EP logic into its own file (#49679)
* the branch is now pointing to main and not to unify-resolve-plan
* Refactor expert parallelism registration and improve documentation
- Consolidated the registration of parallel styles into the `ParallelInterface` class for better organization.
- Updated the `expert_parallel.py` and `tensor_parallel.py` files to streamline the registration process of expert parallel strategies.
- Enhanced documentation for clarity regarding the usage of tensor parallel strategies and their registration.
- Removed redundant code related to `MoeExpertsParallel` and `MoeIdentityParallel` classes, which are now properly registered in the new structure.
* comment
* some models missed the tests EP mixin
* fix copyright
