Rename DigraphDijkstra to DigraphShortestPaths

[William-Kenyon]

Fixes #570, renaming DigraphDijkstra to DigraphShortestPaths, using the new DIGRAPHS_DeclareObsoleteSynonym.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.48%. Comparing base (7c00ce7) to head (0a4f0e9).

Additional details and impacted files

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##             main     #958   +/-   ##
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  Coverage   97.48%   97.48%           
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  Files          53       53           
  Lines       21363    21364    +1     
  Branches      639      639           
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+ Hits        20825    20826    +1     
  Misses        473      473           
  Partials       65       65           

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[james-d-mitchell]

@mtorpey can you please have a look at this.

My initial reaction is that I'm not sure this addresses #570. In particular, if there's duplicate code between DigraphDijkstra and DigraphShortestPath, then this PR does not remove it. Also if we merge this PR, there will be two functions DigraphShortestPath and DigraphShortestPaths which return two rather different outputs. Also it's not completely clear to me that DigraphShortestPaths is an entirely accurate name, given that it does not return all shortest paths from source to target as the name suggests.

Maybe I'm missing something essential, @William-Kenyon if there's context or rationale behind these changes that I'm missing, then please do let me know!

[William-Kenyon]

@james-d-mitchell My renaming follows existing convention: we already have EdgeWeightedDigraphShortestPaths, which returns similar lists of distances and predecessors, and EdgeWeightedDigraphShortestPath which returns in the DigraphPath form. I agree that the wording "paths" is ambiguous, as a user might expect all shortest paths between a source and target, but this could be added in the future under the overload: ...ShortestPaths(digraph, source, target).

The current use of the target parameter is actually as an early exit condition and is not needed anymore, I'll remove it.

As for duplication, DigraphShortestPath uses a BFS, which is slightly faster than DigraphShortestPaths's dijkstras, which is why I didn't refactor them. I realise now however that DigraphShortestPaths is obsolete when its EdgeWeighted... counterpart exists, so I'll make it unweighted and share the BFS of DigraphShortestPath.