feat: add oot parallelism decorator

[akoumpa]

Support registering out-of-tree strategies with a decorator:

from nemo_automodel.components.distributed.parallelizer import ParallelizationStrategy, register_parallel_strategy

@register_parallel_strategy
class MyParallelStrategy(ParallelizationStrategy):
    def parallelize(
        self,
        model: nn.Module,
        ...
    ) -> nn.Module:

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