Properly deprecate TimeSeriesRegressor.partial_fit method

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This PR addresses the improper deprecation of the TimeSeriesRegressor.partial_fit method by:

1. Updating documentation files to use the new update method instead of the deprecated partial_fit:

   • examples/regression/2-advanced-analysis/plot_timeseries_enbpi.py: Updated method calls and print statements
   • notebooks/regression/ts-changepoint.ipynb: Updated all instances of partial_fit usage in code cells and text

2. Adding version number to the deprecation warning: The warning now includes "This method will be removed in v1.1." to follow sklearn deprecation guidelines for the next minor version.

3. Updated test to match the new warning message format.

The partial_fit method has been deprecated for some time but was still being used in documentation examples. The update method provides the same functionality and automatically dispatches to the appropriate internal method based on the chosen strategy (enbpi or aci).

Before:

mapie_enbpi.partial_fit(X_test, y_test)  # Shows deprecation warning without version

After:

mapie_enbpi.update(X_test, y_test)  # Clean, no warnings

All existing functionality is preserved, and the deprecation warning now properly indicates when the method will be removed.

Fixes #699.

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