Create Mixin for block backward sync and deprecate block_backward_sync from Parallel Plugin

[four4fish]

Proposed refactoring or deprecation

Discussed in #9101

Motivation

Parallel plugin should be generic and self-contained. Move reference to DistributedDataParallel from parallel block_backward_sync

Pitch

Discussed in #9101
@ananthsub suggested create interface for this trait
`class PluginWithBlockBackwardSync(ABC):

@contextmanager
@abstractmethod
def block_backward_sync(self) -> Generator:`

Additional context

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