[MNT] Use "segment anomalies" rather than "collective anomalies"

[Tveten]

Replace occurences of "collective anomaly" with "segment anomaly". It is a more precise term:

• Collective anomaly: A group of points that are anomalous when viewed together with respect to the rest of the data. The collective anomaly doesn't need to be a set of contiguous points in time.
• Segment anomaly: A collective anomaly where the anomalous points are contiguous in time, i.e., an interval/segment that is anomalous with respect to the rest of the data.

It is also the most suitable term with respect to "time series segmentation".

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.50%. Comparing base (8f08b83) to head (def6b0d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #51   +/-   ##
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  Coverage   97.50%   97.50%           
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  Files          40       40           
  Lines        1680     1680           
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  Hits         1638     1638           
  Misses         42       42           

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