[DOC] Convert TFT tuning and utils docstrings to numpydoc style

[Siddhazntx]

Reference Issues/PRs

Fixes #2066

What does this implement/fix? Explain your changes.

This PR converts the docstrings in the following files from Google style to the NumPy (numpydoc) style to align with the project's documentation standards:

• pytorch_forecasting/models/temporal_fusion_transformer/tuning.py
• pytorch_forecasting/utils/_utils.py

The changes are strictly limited to documentation and do not alter any functional logic.

What should a reviewer concentrate their feedback on?

• Consistency of the NumPy style formatting.
• Accuracy of the parameter types in the new docstrings.

Did you add any tests for the change?

No new functional tests were added as this is a documentation-only change. However, I verified that the code remains functional and passes all linting requirements.

PR checklist

• The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@           Coverage Diff           @@
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  Coverage        ?   86.63%           
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  Files           ?      165           
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  Hits            ?     8431           
  Misses          ?     1301           
  Partials        ?        0           

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pytest	86.63% <ø> (?)

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