Refactor multihypothesis segmentation handling

[cmalinmayor]

Proposed Change

Make different functions for creating candidate graphs from single and multihypothesis segmentations. This makes it simpler to use in the normal case (one hypothesis), avoiding having to add a dummy hypothesis dimension.
Note: This is a breaking change to the public API, since I renamed all the construct graph functions.

Checklist

Go through these things before merge. Actions should run automatically to test them, but for information on how to run locally, see CONTRIBUTING.md.

• I have added tests that prove that my feature works in various situations or tests the bugfix (if applicable).
• I have checked that the tests pass and I maintained or improved test coverage (if applicable).
• I have written docstrings and checked that they render correctly in the documentation build.
• I have checked that mypy type checking passes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.75%. Comparing base (4ca103e) to head (2ffe2c5).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   87.18%   87.75%   +0.56%     
==========================================
  Files          14       14              
  Lines         437      449      +12     
==========================================
+ Hits          381      394      +13     
+ Misses         56       55       -1     

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[cmalinmayor]

Closes #23

[msschwartz21]

Verbal comments :)