[MNT] stop segmenters changing state in predict

[TonyBagnall]

several segmenters failed the test that predict does not change the state. This PR fixes that. All have fit_is_empty = True. The choice is to not store data or to introduce a fit method. For these three

"FLUSSSegmenter": ["check_non_state_changing_method"],
"InformationGainSegmenter": ["check_non_state_changing_method"],
"GreedyGaussianSegmenter": ["check_non_state_changing_method"],

just stopped storing data not used anywhere.
edit: will leave clasp, used in notebooks

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[baraline]

(Long time I looked at segmentation) For GG and IGTS changes should be OK, but for Fluss, if you change the X you give in predict it won't change the prediction, it feels weird. Couldn't you just remove the self storing of found_cps and the others to avoid the state change in predict ?