Add audio resampling to fix Whisper sampling rate mismatch

[McVyp]

This addresses an issue in the Whisper feature extraction example in Preprocessing Audio Data documentation where the example code doesn't handle sampling rate mismatches.

I encountered a ValueError when using the example code with the MINDS14 dataset (8 kHz) since Whisper requires 16 kHz audio. While the documentation mentions using cast_column for resampling in another section, this approach didn't resolve the error when used with the Whisper feature extractor.

Changes made:

• Updated the prepare_dataset function to explicitly handle sampling rate mismatches
• Added direct resampling with librosa which successfully resolves the error
• Ensured the example works end-to-end with datasets that have different sampling rates

[HuggingFaceDocBuilderDev]

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