[MNT] Fixed wrong type annotations for aeon classes

[shinymack]

Reference Issues/PRs

Fixes #1928

What does this implement/fix? Explain your changes.

Fixed incorrect type hinting in private methods for _TreeNode and PCA

1. Changed type hint for the _find_splits_gain method in _continuous_interval_tree.py from type[_TreeNode] to _TreeNode.
2. Updated the type hint for pcas in _predict_for_estimator and _predict_proba_for_estimator methods in _rotation_forest_classifier.py and _rotation_forest_regressor.py from type[PCA] to PCA.

The changes correct type hints by using class instances instead of class types for _TreeNode and PCA.

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

No

Any other comments?

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