[DOC] Fix inconsistent docstring formatting for issue #809

[an04shu]

Reference Issues/PRs

Fixes #809. This PR addresses inconsistencies in docstring formatting in the aeon.forecasting module.

What does this implement/fix? Explain your changes.

This pull request resolves an issue with inconsistent use of single and double ticks for code references within docstrings across several files. The issue caused references to code elements like int, RandomState, and None to be inconsistently formatted, leading to confusion in the documentation. All references have now been standardized to use double ticks for consistency and clarity in the documentation. The affected files are:

• aeon/forecasting/_dummy.py
• aeon/forecasting/_ets.py
• aeon/forecasting/_regression.py
• aeon/forecasting/base.py

The changes improve the readability and accuracy of the API documentation.

Does your contribution introduce a new dependency? If yes, which one?

No new dependencies

Any other comments?

This PR solely focuses on fixing the formatting issues in the docstrings. No functionality has been changed.

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