Adding type hints for segmentation

[freemansw1]

As part of my broader type hinting efforts (see #74, #341, #337), I've gone through quickly and added type hints to Segmentation. I have avoided type hints on the wrapper functions, as I think we need to ultimately decide what to do with them at some later stage.

As an aside (and I should make an issue for this), Segmentation (especially after the PBC changes, sorry about that) is in desperate need of a deep refactor.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (85f8f3a) 56.35% compared to head (a635af8) 56.40%.

Additional details and impacted files

@@              Coverage Diff              @@
##           RC_v1.5.x     #351      +/-   ##
=============================================
+ Coverage      56.35%   56.40%   +0.05%     
=============================================
  Files             16       16              
  Lines           3384     3388       +4     
=============================================
+ Hits            1907     1911       +4     
  Misses          1477     1477              

Flag	Coverage Δ
unittests	56.40% <100.00%> (+0.05%)	⬆️

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Files	Coverage Δ
tobac/segmentation.py	92.89% <100.00%> (+0.07%)	⬆️

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[w-k-jones]

As an aside (and I should make an issue for this), Segmentation (especially after the PBC changes, sorry about that) is in desperate need of a deep refactor.

I agree, and although we will definitely do this as part of the conversion to xarray it may be worthwhile to do a couple of passes first, both to fix the worst code smells and break things down into more manageable sized functions

[JuliaKukulies]

Looks good!