fix(generator): don't truncate datetime field precision

[Oblynx]

closes #804

• [ ] Unit tests for the changes exist
• [ ] Tests pass without significant drop in coverage
• [ ] Documentation reflects changes where applicable
• [ ] Test snapshots have been updated if applicable

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Change Summary

Please summarise the changes this pull request is making here.

Checklist

• [ ] Unit tests for the changes exist
• [ ] Tests pass without significant drop in coverage
• [ ] Documentation reflects changes where applicable
• [ ] Test snapshots have been updated if applicable

Agreement

By submitting this pull request, I confirm that you can use, modify, copy and redistribute this contribution, under the terms of your choice.

[Oblynx]

@RobertCraigie do you need anything more from me here?

[RobertCraigie]

It would be great to have a test for this case, here's a link to the docs on how to write tests - let me know if you have any questions!