Fix `ImportError` and `NameError` in `examples/run_simple_mcore_train_loop.py`

[marksverdhei]

What does this PR do ?

This PR fixes two breaking bugs (ImportError and NameError) in examples/run_simple_train_loop.py that were introduced when type hints were added.

Resolves #1979

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• [ ] I want this PR in a versioned release and have added the appropriate Milestone (e.g., Core 0.8)
• [ ] I have added relevant unit tests
• [ ] I have added relevant functional tests
• [x] I have added proper typing to my code Typing guidelines
• [x] I have added relevant documentation
• [ ] I have run the autoformatter.sh on my PR

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[marksverdhei]

@ananthsub Should this be merged?

[simondong1]

@ananthsub Should this be merged?

please merge

[theothermike]

/ok to test ee29372652a2114118e2b9c56d719d7ebdecce2e

[theothermike]

/ok to test 518bb1f7f272d399f113de233bbb8e59ffacf2c7

[theothermike]

/ok to test 47652b01ff036d64f447a6af0f9f724a8c0f2091

[theothermike]

/ok to test 5c8f311aa4f62378d153934aaf3215b9651c96cb

[theothermike]

/ok to test 1130e28397277897efd11b539ef05d781d1a256b

[chtruong814]

/ok to test 8373b7a

[github-actions[bot]]

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[marksverdhei]