*Issue #, if available:* #425
*Description of changes:*
- Add `freq: str | None` parameter to `predict_df` methods. This can
only be set in combination with `validate_inputs=False`. If specified,
the user-provided `freq` will be used instead of the tryin to infer the
`freq` from the data.
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copy, and redistribute this contribution, under the terms of your
choice.
*Issue #, if available:*
*Description of changes:* This PR improves test coverage by adding unit
tests for `df_utils`. Previously these methods were only being tested as
part of Chronos-2 integration tests.
By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.
