[BUG] SFA.get_words() and SFAFast.get_words() crash for any normal sliding-window configuration

[patrickzib]

Fixes #3537

SFA.get_words() and SFAFast.get_words() crashed when window_size < n_timepoints (the normal sliding-window configuration). Now fixed

Changes

• aeon/transformations/collection/dictionary_based/_sfa.py:
• aeon/transformations/collection/dictionary_based/_sfa_fast.py
• aeon/transformations/collection/dictionary_based/tests/test_sfa.py: Add new regression tests covering sliding window

Testing

All tests in test_sfa.py pass

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[TonyBagnall]

thanks for the fix, but new get_chars helper mutates the input words array while decoding it, by shifting each word in place. A getter shouldnt mutate the state of the object imo