Align Remote function classes to ModelTrainer: Include training_plan_arn to remote function classes @remote decorator and RemoteExecutor

**Describe the feature you'd like**
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ModelTrainer and Estimator classes currently support training_plan_arn, in order to run training workload by leveraging the instances included in the plan. This functionality is not currently available with remote function classes, which is adopted by customer to start prototyping workloads on Amazon SageMaker.

**How would this feature be used? Please describe.**
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```
@remote(
...
training_plan_arn="arn.1234....."
)
def train(args):
pass
```

**Describe alternatives you've considered**
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There are no alternative solutions

**Additional context**
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Start by comparing how ModelTrainer and Estimator accept and use training_plan_arn, then trace the @remote decorator and RemoteExecutor paths for equivalent configuration. Define the expected flow for the ARN from decorator arguments into remote execution, and add coverage showing that a remote function can launch with the specified training plan.

Written by the indexing model from the issue text.