Fixes #8580

This pull request introduces a new feature to the IndividualBOSS classifier in the sktime library, allowing it to optionally store histograms of words during the fit process. This feature is controlled by a new parameter, store_histogram, and is accompanied by updates to the class attributes, methods, and corresponding tests.

Enhancements to IndividualBOSS:

• New Parameter and Attribute:

  • Added the store_histogram parameter (default: False) to the __init__ method to control whether histograms of words are stored during fit. [1] [2]
  • Introduced a new attribute, histograms_, to store the word histograms for each time series instance when store_histogram is enabled. [1] [2]

• New Method for Histogram Creation:

  • Added the _create_histograms method to generate and store histograms based on the transformed data, using the transformer's vocabulary. This method is invoked during _fit if store_histogram is True.

Unit Tests:

• Testing store_histogram=True:

  • Added test_individual_boss_histograms to verify the type and size of the histograms_ attribute when store_histogram is enabled. It ensures that the histograms are stored as a list of dictionaries with valid keys and values.

• Testing store_histogram=False:

  • Added test_individual_boss_no_histograms to confirm that the histograms_ attribute remains an empty list when store_histogram is disabled.Introduces the 'store_histogram' parameter to IndividualBOSS, allowing users to optionally store word histograms for each training instance. Updates the class to document and implement this feature, and adds tests to verify correct behavior when histograms are stored or omitted.

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