[Testing] Create Integration tests to test Batch Checkpointing behaviour

Migration from https://github.com/aws/aws-durable-execution-sdk-python-testing/issues/77

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Test the following:

- Step semantics (at least / at most)
- Thundering herd within parallel/map
- Size of checkpoints greater than size limit
- Synchronous checkpointing when appropriate (see readme on sdk package)
